From 95c4e7521db95a021f5920fab7a0e19d13a2090e Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Wed, 18 Mar 2026 19:25:41 +0000
Subject: [PATCH 01/13] Fix address debug exercise

---
 Sprint-2/debug/address.js | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..7385b5e4c 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,8 +1,9 @@
 // Predict and explain first...
 
 // This code should log out the houseNumber from the address object
-// but it isn't working...
-// Fix anything that isn't working
+// but it isn't working.
+// The bug was that the code tried to access the object using index [0].
+// Objects use property names instead of numeric indexes.
 
 const address = {
   houseNumber: 42,
@@ -12,4 +13,5 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+// Correctly access the houseNumber property
+console.log(`My house number is ${address.houseNumber}`);

From a4f6039b26888739b582eb7d329b9b3eb82f7c65 Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Wed, 18 Mar 2026 19:29:31 +0000
Subject: [PATCH 02/13] Fix author debug exercise

---
 Sprint-2/debug/author.js | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..5145b976a 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,7 +1,8 @@
 // Predict and explain first...
 
 // This program attempts to log out all the property values in the object.
-// But it isn't working. Explain why first and then fix the problem
+// It was not working because plain objects are not iterable with for...of.
+// To loop through the values, we first convert them into an array using Object.values().
 
 const author = {
   firstName: "Zadie",
@@ -11,6 +12,7 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+// Loop through all the values in the object
+for (const value of Object.values(author)) {
   console.log(value);
 }

From 6543d0ff151df6a9b596e5f1fd423c5d388ddd43 Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Wed, 18 Mar 2026 19:32:11 +0000
Subject: [PATCH 03/13] Fix recipe debug exercise

---
 Sprint-2/debug/recipe.js | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..7b43deb42 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,8 +1,9 @@
 // Predict and explain first...
 
 // This program should log out the title, how many it serves and the ingredients.
-// Each ingredient should be logged on a new line
-// How can you fix it?
+// Each ingredient should be logged on a new line.
+// The original code tried to print the entire recipe object,
+// which resulted in "[object Object]" instead of the ingredients.
 
 const recipe = {
   title: "bruschetta",
@@ -10,6 +11,11 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+// Print title and serving size
+console.log(`${recipe.title} serves ${recipe.serves}`);
+console.log("ingredients:");
+
+// Loop through the ingredients array and print each one
+for (const ingredient of recipe.ingredients) {
+  console.log(ingredient);
+}

From eb9641b742609bd8eeecf1d778a7e18cc5f098b3 Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Wed, 18 Mar 2026 19:53:59 +0000
Subject: [PATCH 04/13] Implement contains function and tests

---
 Sprint-2/implement/contains.js      | 26 +++++++++++++++++-
 Sprint-2/implement/contains.test.js | 42 +++++++++++++----------------
 2 files changed, 44 insertions(+), 24 deletions(-)

diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..1527711b2 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,27 @@
-function contains() {}
+/**
+ * contains()
+ *
+ * Checks whether an object contains a specific property.
+ *
+ * @param {object} obj - The object to check.
+ * @param {string} propertyName - The property name we want to check.
+ * @returns {boolean} True if the property exists, otherwise false.
+ */
+
+function contains(obj, propertyName) {
+  // Validate that obj is actually an object
+  // and not null or an array
+  if (obj === null || typeof obj !== "object" || Array.isArray(obj)) {
+    return false;
+  }
+
+  // Validate propertyName
+  if (typeof propertyName !== "string" || propertyName.length === 0) {
+    return false;
+  }
+
+  // Check if the object has the property as its own key
+  return Object.prototype.hasOwnProperty.call(obj, propertyName);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..67bbc115f 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -4,32 +4,28 @@ const contains = require("./contains.js");
 Implement a function called contains that checks an object contains a
 particular property
 
-E.g. contains({a: 1, b: 2}, 'a') // returns true
-as the object contains a key of 'a'
-
-E.g. contains({a: 1, b: 2}, 'c') // returns false
-as the object doesn't contains a key of 'c'
+E.g. contains({a: 1, b: 2}, "a") // returns true
+E.g. contains({a: 1, b: 2}, "c") // returns false
 */
 
-// Acceptance criteria:
-
-// Given a contains function
-// When passed an object and a property name
-// Then it should return true if the object contains the property, false otherwise
+describe("contains()", () => {
+  test("returns false for an empty object", () => {
+    expect(contains({}, "a")).toBe(false);
+  });
 
-// Given an empty object
-// When passed to contains
-// Then it should return false
-test.todo("contains on empty object returns false");
+  test("returns true when the property exists", () => {
+    expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+  });
 
-// Given an object with properties
-// When passed to contains with an existing property name
-// Then it should return true
+  test("returns false when the property does not exist", () => {
+    expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+  });
 
-// Given an object with properties
-// When passed to contains with a non-existent property name
-// Then it should return false
+  test("returns false when given an array", () => {
+    expect(contains(["a", "b"], "0")).toBe(false);
+  });
 
-// Given invalid parameters like an array
-// When passed to contains
-// Then it should return false or throw an error
+  test("returns false when given null", () => {
+    expect(contains(null, "a")).toBe(false);
+  });
+});

From de8ca144413363cb13e969b415be8cc9001ec085 Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Wed, 18 Mar 2026 20:03:59 +0000
Subject: [PATCH 05/13] Implement lookup function and tests

---
 Sprint-2/implement/lookup.js      | 36 ++++++++++++++++-
 Sprint-2/implement/lookup.test.js | 65 +++++++++++++++----------------
 2 files changed, 66 insertions(+), 35 deletions(-)

diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..9e424317c 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,37 @@
-function createLookup() {
-  // implementation here
+/**
+ * createLookup()
+ *
+ * Converts an array of [key, value] pairs into a lookup object.
+ *
+ * Example:
+ * [['US', 'USD'], ['CA', 'CAD']]
+ *
+ * Returns:
+ * { US: 'USD', CA: 'CAD' }
+ */
+
+function createLookup(pairs) {
+  // Ensure the input is an array
+  if (!Array.isArray(pairs)) {
+    throw new Error("Expected an array of pairs");
+  }
+
+  const lookup = {};
+
+  // Loop through each pair
+  for (const pair of pairs) {
+    // Validate that each pair has exactly two values
+    if (!Array.isArray(pair) || pair.length !== 2) {
+      throw new Error("Each item must be a [key, value] pair");
+    }
+
+    const [key, value] = pair;
+
+    // Add to lookup object
+    lookup[key] = value;
+  }
+
+  return lookup;
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..931d21c94 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,35 +1,34 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
-/*
-
-Create a lookup object of key value pairs from an array of code pairs
-
-Acceptance Criteria:
-
-Given
- - An array of arrays representing country code and currency code pairs
-   e.g. [['US', 'USD'], ['CA', 'CAD']]
-
-When
- - createLookup function is called with the country-currency array as an argument
-
-Then
- - It should return an object where:
- - The keys are the country codes
- - The values are the corresponding currency codes
-
-Example
-Given: [['US', 'USD'], ['CA', 'CAD']]
-
-When
-createLookup(countryCurrencyPairs) is called
-
-Then
-It should return:
- {
-   'US': 'USD',
-   'CA': 'CAD'
- }
-*/
+describe("createLookup()", () => {
+  test("creates a country currency code lookup for multiple codes", () => {
+    const pairs = [
+      ["US", "USD"],
+      ["CA", "CAD"],
+    ];
+
+    expect(createLookup(pairs)).toEqual({
+      US: "USD",
+      CA: "CAD",
+    });
+  });
+
+  test("returns an empty object for an empty array", () => {
+    expect(createLookup([])).toEqual({});
+  });
+
+  test("overwrites duplicate keys with the last value", () => {
+    const pairs = [
+      ["US", "USD"],
+      ["US", "USN"],
+    ];
+
+    expect(createLookup(pairs)).toEqual({
+      US: "USN",
+    });
+  });
+
+  test("throws an error when input is not an array", () => {
+    expect(() => createLookup("invalid")).toThrow();
+  });
+});

From ce21823a9f842c0ad10ba870ce95ba2c749855f6 Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Wed, 18 Mar 2026 20:13:22 +0000
Subject: [PATCH 06/13] Implement tally function and tests

---
 Sprint-2/implement/tally.js      | 32 ++++++++++++++++++++-
 Sprint-2/implement/tally.test.js | 49 ++++++++++++++------------------
 2 files changed, 52 insertions(+), 29 deletions(-)

diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..d6ee073a8 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,33 @@
-function tally() {}
+/**
+ * tally()
+ *
+ * Counts how many times each item appears in an array.
+ *
+ * Example:
+ * tally(['a','a','b','c'])
+ * returns { a: 2, b: 1, c: 1 }
+ */
+
+function tally(items) {
+  // Validate input
+  if (!Array.isArray(items)) {
+    throw new Error("Expected an array");
+  }
+
+  const counts = {};
+
+  // Loop through each item in the array
+  for (const item of items) {
+    // If the item already exists in the object, increase the count
+    if (counts[item]) {
+      counts[item] += 1;
+    } else {
+      // Otherwise initialise it
+      counts[item] = 1;
+    }
+  }
+
+  return counts;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..6d80fc996 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -1,34 +1,27 @@
 const tally = require("./tally.js");
 
-/**
- * tally array
- *
- * In this task, you'll need to implement a function called tally
- * that will take a list of items and count the frequency of each item
- * in an array
- *
- * For example:
- *
- * tally(['a']), target output: { a: 1 }
- * tally(['a', 'a', 'a']), target output: { a: 3 }
- * tally(['a', 'a', 'b', 'c']), target output: { a : 2, b: 1, c: 1 }
- */
+describe("tally()", () => {
+  test("returns an empty object for an empty array", () => {
+    expect(tally([])).toEqual({});
+  });
 
-// Acceptance criteria:
+  test("counts a single item", () => {
+    expect(tally(["a"])).toEqual({ a: 1 });
+  });
 
-// Given a function called tally
-// When passed an array of items
-// Then it should return an object containing the count for each unique item
+  test("counts repeated items", () => {
+    expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+  });
 
-// Given an empty array
-// When passed to tally
-// Then it should return an empty object
-test.todo("tally on an empty array returns an empty object");
+  test("counts multiple different items", () => {
+    expect(tally(["a", "a", "b", "c"])).toEqual({
+      a: 2,
+      b: 1,
+      c: 1,
+    });
+  });
 
-// Given an array with duplicate items
-// When passed to tally
-// Then it should return counts for each unique item
-
-// Given an invalid input like a string
-// When passed to tally
-// Then it should throw an error
+  test("throws an error for invalid input", () => {
+    expect(() => tally("not-an-array")).toThrow();
+  });
+});

From 7aa84ed0cee14bf7490216e5a9750fbb82140b9f Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Wed, 18 Mar 2026 20:18:48 +0000
Subject: [PATCH 07/13] Fix querystring parser and add edge case tests

---
 Sprint-2/implement/querystring.js      | 35 +++++++++++++++++--
 Sprint-2/implement/querystring.test.js | 48 +++++++++++++++++++++-----
 2 files changed, 73 insertions(+), 10 deletions(-)

diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..617ea20e3 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,12 +1,43 @@
+/**
+ * parseQueryString()
+ *
+ * Parses a query string into an object of key-value pairs.
+ *
+ * Example:
+ * parseQueryString("name=Richard&city=Sheffield")
+ * returns { name: "Richard", city: "Sheffield" }
+ */
+
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+
+  // Return an empty object if the input is an empty string
+  if (typeof queryString !== "string" || queryString.length === 0) {
     return queryParams;
   }
+
+  // Split the full query string into key-value pairs
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    // Skip empty pairs, for example from a trailing "&"
+    if (pair === "") {
+      continue;
+    }
+
+    // Find the position of the first "="
+    const separatorIndex = pair.indexOf("=");
+
+    // If there is no "=" sign, treat it as a key with an empty value
+    if (separatorIndex === -1) {
+      queryParams[pair] = "";
+      continue;
+    }
+
+    // Extract the key and everything after the first "=" as the value
+    const key = pair.slice(0, separatorIndex);
+    const value = pair.slice(separatorIndex + 1);
+
     queryParams[key] = value;
   }
 
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..431d6fd13 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -1,12 +1,44 @@
-// In the prep, we implemented a function to parse query strings.
-// Unfortunately, it contains several bugs!
-// Below is one test case for an edge case the implementation doesn't handle well.
-// Fix the implementation for this test, and try to think of as many other edge cases as possible - write tests and fix those too.
+const parseQueryString = require("./querystring.js");
 
-const parseQueryString = require("./querystring.js")
+describe("parseQueryString()", () => {
+  test("parses querystring values containing =", () => {
+    expect(parseQueryString("equation=x=y+1")).toEqual({
+      equation: "x=y+1",
+    });
+  });
+
+  test("returns an empty object for an empty string", () => {
+    expect(parseQueryString("")).toEqual({});
+  });
+
+  test("parses a single key-value pair", () => {
+    expect(parseQueryString("name=Richard")).toEqual({
+      name: "Richard",
+    });
+  });
+
+  test("parses multiple key-value pairs", () => {
+    expect(parseQueryString("name=Richard&city=Sheffield")).toEqual({
+      name: "Richard",
+      city: "Sheffield",
+    });
+  });
+
+  test("handles a key with an empty value", () => {
+    expect(parseQueryString("name=")).toEqual({
+      name: "",
+    });
+  });
+
+  test("handles a key with no equals sign", () => {
+    expect(parseQueryString("name")).toEqual({
+      name: "",
+    });
+  });
 
-test("parses querystring values containing =", () => {
-  expect(parseQueryString("equation=x=y+1")).toEqual({
-    "equation": "x=y+1",
+  test("ignores an empty trailing pair", () => {
+    expect(parseQueryString("name=Richard&")).toEqual({
+      name: "Richard",
+    });
   });
 });

From af702c47d6e31e290db3de14034852cf2656c477 Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Wed, 18 Mar 2026 20:29:11 +0000
Subject: [PATCH 08/13] Fix invert implementation and add tests

---
 Sprint-2/interpret/invert.js      | 79 ++++++++++++++++++++++++++-----
 Sprint-2/interpret/invert.test.js | 20 ++++++++
 2 files changed, 86 insertions(+), 13 deletions(-)
 create mode 100644 Sprint-2/interpret/invert.test.js

diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..cce52f2fb 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -4,26 +4,79 @@
 // When invert is passed this object
 // Then it should swap the keys and values in the object
 
-// E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
+// Example:
+// invert({ x: 10, y: 20 })
+// should return:
+// { "10": "x", "20": "y" }
 
-function invert(obj) {
-  const invertedObj = {};
+/*
+a) What is the current return value when invert({ a: 1 }) is called?
 
-  for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
-  }
+Current output:
+{ key: 1 }
 
-  return invertedObj;
+Reason:
+The code uses invertedObj.key which creates a property literally called "key"
+instead of using the variable key.
+
+---------------------------------------------------
+
+b) What is the current return value when invert({ a: 1, b: 2 }) is called?
+
+Current output:
+{ key: 2 }
+
+Reason:
+The second iteration overwrites the first value because the property name
+is always "key".
+
+---------------------------------------------------
+
+c) What is the target return value when invert({ a: 1, b: 2 }) is called?
+
+Expected output:
+{
+  "1": "a",
+  "2": "b"
 }
 
-// a) What is the current return value when invert is called with { a : 1 }
+Keys and values should be swapped.
+
+---------------------------------------------------
 
-// b) What is the current return value when invert is called with { a: 1, b: 2 }
+d) What does Object.entries return? Why is it needed?
 
-// c) What is the target return value when invert is called with {a : 1, b: 2}
+Object.entries(obj) converts an object into an array of [key, value] pairs.
 
-// c) What does Object.entries return? Why is it needed in this program?
+Example:
+Object.entries({ a: 1, b: 2 })
 
-// d) Explain why the current return value is different from the target output
+returns:
+[
+  ["a", 1],
+  ["b", 2]
+]
+
+This allows us to loop through object properties using for...of.
+
+---------------------------------------------------
+
+e) Why is the current return value different from the target output?
+
+Because invertedObj.key uses the literal property name "key".
+To use the value dynamically as the key, we must use bracket notation:
+invertedObj[value] = key;
+*/
+
+function invert(obj) {
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    // Correct implementation: swap key and value
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
 
-// e) Fix the implementation of invert (and write tests to prove it's fixed!)
+module.exports = invert;
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..8b269233e
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,20 @@
+const invert = require("./invert.js");
+
+describe("invert()", () => {
+  test("inverts a single key-value pair", () => {
+    expect(invert({ a: 1 })).toEqual({
+      1: "a",
+    });
+  });
+
+  test("inverts multiple key-value pairs", () => {
+    expect(invert({ a: 1, b: 2 })).toEqual({
+      1: "a",
+      2: "b",
+    });
+  });
+
+  test("returns an empty object for empty input", () => {
+    expect(invert({})).toEqual({});
+  });
+});

From 12fb2314c3cb1a504db5f5019c504b723bc36e43 Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Wed, 18 Mar 2026 20:40:38 +0000
Subject: [PATCH 09/13] Complete stretch exercises for Sprint 2

---
 Sprint-2/stretch/count-words.js | 40 ++++++++++++++++-----------------
 Sprint-2/stretch/mode.js        | 32 +++++++++++++-------------
 2 files changed, 34 insertions(+), 38 deletions(-)

diff --git a/Sprint-2/stretch/count-words.js b/Sprint-2/stretch/count-words.js
index 8e85d19d7..dbea38d13 100644
--- a/Sprint-2/stretch/count-words.js
+++ b/Sprint-2/stretch/count-words.js
@@ -1,28 +1,26 @@
-/*
-  Count the number of times a word appears in a given string.
+function countWords(text) {
+  if (typeof text !== "string") {
+    throw new Error("Input must be a string");
+  }
 
-  Write a function called countWords that
-    - takes a string as an argument
-    - returns an object where
-          - the keys are the words from the string and
-          - the values are the number of times the word appears in the string
+  // remove punctuation and make lowercase
+  const cleanedText = text.toLowerCase().replace(/[.,!?]/g, "");
 
-  Example
-  If we call countWords like this:
+  const words = cleanedText.split(/\s+/);
 
-  countWords("you and me and you") then the target output is { you: 2, and: 2, me: 1 }
+  const counts = {};
 
-  To complete this exercise you should understand
-    - Strings and string manipulation
-    - Loops
-    - Comparison inside if statements
-    - Setting values on an object
+  for (const word of words) {
+    if (!word) continue;
 
-## Advanced challenges
+    if (counts[word]) {
+      counts[word]++;
+    } else {
+      counts[word] = 1;
+    }
+  }
 
-1. Remove all of the punctuation (e.g. ".", ",", "!", "?") to tidy up the results
+  return counts;
+}
 
-2. Ignore the case of the words to find more unique words. e.g. (A === a, Hello === hello)
-
-3. Order the results to find out which word is the most common in the input
-*/
+module.exports = countWords;
diff --git a/Sprint-2/stretch/mode.js b/Sprint-2/stretch/mode.js
index 3f7609d79..bef5f3200 100644
--- a/Sprint-2/stretch/mode.js
+++ b/Sprint-2/stretch/mode.js
@@ -1,18 +1,7 @@
-// You are given an implementation of calculateMode
+function trackFrequencies(list) {
+  const freqs = new Map();
 
-// calculateMode's implementation can be broken down into two stages:
-
-// Stage 1. One part of the code tracks the frequency of each value
-// Stage 2. The other part finds the value with the highest frequency
-
-// refactor calculateMode by splitting up the code
-// into smaller functions using the stages above
-
-function calculateMode(list) {
-  // track frequency of each value
-  let freqs = new Map();
-
-  for (let num of list) {
+  for (const num of list) {
     if (typeof num !== "number") {
       continue;
     }
@@ -20,17 +9,26 @@ function calculateMode(list) {
     freqs.set(num, (freqs.get(num) || 0) + 1);
   }
 
-  // Find the value with the highest frequency
+  return freqs;
+}
+
+function findMode(freqs) {
   let maxFreq = 0;
   let mode;
-  for (let [num, freq] of freqs) {
+
+  for (const [num, freq] of freqs) {
     if (freq > maxFreq) {
-      mode = num;
       maxFreq = freq;
+      mode = num;
     }
   }
 
   return maxFreq === 0 ? NaN : mode;
 }
 
+function calculateMode(list) {
+  const freqs = trackFrequencies(list);
+  return findMode(freqs);
+}
+
 module.exports = calculateMode;

From e296ae7effaeba30b56d0b0529ff74d4d1c11d54 Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Wed, 18 Mar 2026 21:31:10 +0000
Subject: [PATCH 10/13] Fix test file location for countWords

---
 Sprint-2/stretch/count-words.test.js | 31 ++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 Sprint-2/stretch/count-words.test.js

diff --git a/Sprint-2/stretch/count-words.test.js b/Sprint-2/stretch/count-words.test.js
new file mode 100644
index 000000000..29ec3433f
--- /dev/null
+++ b/Sprint-2/stretch/count-words.test.js
@@ -0,0 +1,31 @@
+const countWords = require("./count-words.js");
+
+describe("countWords()", () => {
+  test("counts repeated words", () => {
+    expect(countWords("you and me and you")).toEqual({
+      you: 2,
+      and: 2,
+      me: 1,
+    });
+  });
+
+  test("handles punctuation stuck to words", () => {
+    expect(countWords("Hello,World! Hello World!")).toEqual({
+      hello: 2,
+      world: 2,
+    });
+  });
+
+  test("handles inherited-property words safely", () => {
+    expect(countWords("constructor constructor")).toEqual({
+      constructor: 2,
+    });
+  });
+
+  test("handles extra spaces correctly", () => {
+    expect(countWords("          Hello World      ")).toEqual({
+      hello: 1,
+      world: 1,
+    });
+  });
+});

From a22ed15d12c368d44d0e5f4f3529ced09691ac7c Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Thu, 19 Mar 2026 01:49:14 +0000
Subject: [PATCH 11/13] Address mentor feedback for sprint 1 data groups

---
 Sprint-1/fix/median.js            | 27 ++++++++++++++++++++++++---
 Sprint-1/implement/dedupe.js      | 18 +++++++++++++++++-
 Sprint-1/implement/dedupe.test.js | 24 ++++++++++++++++++++++--
 Sprint-1/implement/max.js         | 12 ++++++++++++
 Sprint-1/implement/max.test.js    | 23 +++++++++++++++++++++--
 Sprint-1/implement/sum.js         | 12 ++++++++++++
 Sprint-1/implement/sum.test.js    | 19 ++++++++++++++++++-
 7 files changed, 126 insertions(+), 9 deletions(-)

diff --git a/Sprint-1/fix/median.js b/Sprint-1/fix/median.js
index b22590bc6..01b74c403 100644
--- a/Sprint-1/fix/median.js
+++ b/Sprint-1/fix/median.js
@@ -6,9 +6,30 @@
 // or 'list' has mixed values (the function is expected to sort only numbers).
 
 function calculateMedian(list) {
-  const middleIndex = Math.floor(list.length / 2);
-  const median = list.splice(middleIndex, 1)[0];
-  return median;
+  // Return null immediately if the input is not an array
+  if (!Array.isArray(list)) {
+    return null;
+  }
+
+  // filter() returns a new array, so this does not modify the original input
+  const numbersOnly = list.filter((item) => Number.isFinite(item));
+
+  // Return null if there are no numeric values
+  if (numbersOnly.length === 0) {
+    return null;
+  }
+
+  // Safe to sort directly because numbersOnly is already a new array
+  const sortedNumbers = numbersOnly.sort((a, b) => a - b);
+  const middleIndex = Math.floor(sortedNumbers.length / 2);
+
+  // Even number of values: return the average of the two middle values
+  if (sortedNumbers.length % 2 === 0) {
+    return (sortedNumbers[middleIndex - 1] + sortedNumbers[middleIndex]) / 2;
+  }
+
+  // Odd number of values: return the middle value
+  return sortedNumbers[middleIndex];
 }
 
 module.exports = calculateMedian;
diff --git a/Sprint-1/implement/dedupe.js b/Sprint-1/implement/dedupe.js
index 781e8718a..f8494b4a5 100644
--- a/Sprint-1/implement/dedupe.js
+++ b/Sprint-1/implement/dedupe.js
@@ -1 +1,17 @@
-function dedupe() {}
+// Return a new array with duplicate values removed.
+// Keep the first occurrence of each value.
+
+function dedupe(elements) {
+  const uniqueElements = [];
+
+  for (const element of elements) {
+    // Add the element only if it is not already in the result array
+    if (!uniqueElements.includes(element)) {
+      uniqueElements.push(element);
+    }
+  }
+
+  return uniqueElements;
+}
+
+module.exports = dedupe;
diff --git a/Sprint-1/implement/dedupe.test.js b/Sprint-1/implement/dedupe.test.js
index 23e0f8638..f4336cc48 100644
--- a/Sprint-1/implement/dedupe.test.js
+++ b/Sprint-1/implement/dedupe.test.js
@@ -2,7 +2,7 @@ const dedupe = require("./dedupe.js");
 /*
 Dedupe Array
 
-📖 Dedupe means **deduplicate**
+ Dedupe means deduplicate
 
 In this kata, you will need to deduplicate the elements of an array
 
@@ -16,12 +16,32 @@ E.g. dedupe([1, 2, 1]) target output: [1, 2]
 // Given an empty array
 // When passed to the dedupe function
 // Then it should return an empty array
-test.todo("given an empty array, it returns an empty array");
+test("given an empty array, it returns an empty array", () => {
+  expect(dedupe([])).toEqual([]);
+});
 
 // Given an array with no duplicates
 // When passed to the dedupe function
 // Then it should return a copy of the original array
+test("given an array with no duplicates, it returns a copy of the original array", () => {
+  const input = [1, 2, 3];
+  const result = dedupe(input);
+
+  expect(result).toEqual(input);
+  expect(result).not.toBe(input);
+});
 
 // Given an array with strings or numbers
 // When passed to the dedupe function
 // Then it should remove the duplicate values, preserving the first occurence of each element
+test("given an array with duplicate strings, removes duplicates and preserves first occurrence", () => {
+  expect(dedupe(["a", "a", "a", "b", "b", "c"])).toEqual(["a", "b", "c"]);
+});
+
+test("given an array with duplicate numbers, removes duplicates and preserves first occurrence", () => {
+  expect(dedupe([5, 1, 1, 2, 3, 2, 5, 8])).toEqual([5, 1, 2, 3, 8]);
+});
+
+test("given a mixed duplicate order, removes duplicates and preserves first occurrence", () => {
+  expect(dedupe([1, 2, 1])).toEqual([1, 2]);
+});
diff --git a/Sprint-1/implement/max.js b/Sprint-1/implement/max.js
index 6dd76378e..b9017f0bf 100644
--- a/Sprint-1/implement/max.js
+++ b/Sprint-1/implement/max.js
@@ -1,4 +1,16 @@
+// Find the largest numerical value in an array.
+// Non-number values should be ignored.
+
 function findMax(elements) {
+  let maxValue = -Infinity;
+
+  for (const element of elements) {
+    if (Number.isFinite(element) && element > maxValue) {
+      maxValue = element;
+    }
+  }
+
+  return maxValue;
 }
 
 module.exports = findMax;
diff --git a/Sprint-1/implement/max.test.js b/Sprint-1/implement/max.test.js
index 82f18fd88..ebb57b922 100644
--- a/Sprint-1/implement/max.test.js
+++ b/Sprint-1/implement/max.test.js
@@ -15,29 +15,48 @@ const findMax = require("./max.js");
 // Given an empty array
 // When passed to the max function
 // Then it should return -Infinity
-// Delete this test.todo and replace it with a test.
-test.todo("given an empty array, returns -Infinity");
+test("given an empty array, returns -Infinity", () => {
+  expect(findMax([])).toBe(-Infinity);
+});
 
 // Given an array with one number
 // When passed to the max function
 // Then it should return that number
+test("given an array with one number, returns that number", () => {
+  expect(findMax([42])).toBe(42);
+});
 
 // Given an array with both positive and negative numbers
 // When passed to the max function
 // Then it should return the largest number overall
+test("given an array with positive and negative numbers, returns the largest number", () => {
+  expect(findMax([-10, 3, 25, -1])).toBe(25);
+});
 
 // Given an array with just negative numbers
 // When passed to the max function
 // Then it should return the closest one to zero
+test("given an array with only negative numbers, returns the largest one", () => {
+  expect(findMax([-9, -2, -15, -4])).toBe(-2);
+});
 
 // Given an array with decimal numbers
 // When passed to the max function
 // Then it should return the largest decimal number
+test("given an array with decimal numbers, returns the largest decimal", () => {
+  expect(findMax([1.2, 3.8, 2.4])).toBe(3.8);
+});
 
 // Given an array with non-number values
 // When passed to the max function
 // Then it should return the max and ignore non-numeric values
+test("given an array with non-number values, ignores them and returns the max", () => {
+  expect(findMax(["hey", 10, "300", "hi", 60, 10])).toBe(60);
+});
 
 // Given an array with only non-number values
 // When passed to the max function
 // Then it should return the least surprising value given how it behaves for all other inputs
+test("given an array with only non-number values, returns -Infinity", () => {
+  expect(findMax(["apple", null, undefined, "banana"])).toBe(-Infinity);
+});
diff --git a/Sprint-1/implement/sum.js b/Sprint-1/implement/sum.js
index 9062aafe3..59f5ecc83 100644
--- a/Sprint-1/implement/sum.js
+++ b/Sprint-1/implement/sum.js
@@ -1,4 +1,16 @@
+// Sum the numerical values in an array.
+// Non-number values should be ignored.
+
 function sum(elements) {
+  let total = 0;
+
+  for (const element of elements) {
+    if (Number.isFinite(element)) {
+      total += element;
+    }
+  }
+
+  return total;
 }
 
 module.exports = sum;
diff --git a/Sprint-1/implement/sum.test.js b/Sprint-1/implement/sum.test.js
index dd0a090ca..0698757ef 100644
--- a/Sprint-1/implement/sum.test.js
+++ b/Sprint-1/implement/sum.test.js
@@ -13,24 +13,41 @@ const sum = require("./sum.js");
 // Given an empty array
 // When passed to the sum function
 // Then it should return 0
-test.todo("given an empty array, returns 0")
+test("given an empty array, returns 0", () => {
+  expect(sum([])).toBe(0);
+});
 
 // Given an array with just one number
 // When passed to the sum function
 // Then it should return that number
+test("given an array with one number, returns that number", () => {
+  expect(sum([7])).toBe(7);
+});
 
 // Given an array containing negative numbers
 // When passed to the sum function
 // Then it should still return the correct total sum
+test("given an array with negative numbers, returns the correct sum", () => {
+  expect(sum([-5, 10, -2])).toBe(3);
+});
 
 // Given an array with decimal/float numbers
 // When passed to the sum function
 // Then it should return the correct total sum
+test("given an array with decimal numbers, returns the correct sum", () => {
+  expect(sum([1.2, 0.6, 0.005])).toBeCloseTo(1.805, 10);
+});
 
 // Given an array containing non-number values
 // When passed to the sum function
 // Then it should ignore the non-numerical values and return the sum of the numerical elements
+test("given an array with non-number values, ignores them and sums only numbers", () => {
+  expect(sum(["hey", 10, "hi", 60, 10])).toBe(80);
+});
 
 // Given an array with only non-number values
 // When passed to the sum function
 // Then it should return the least surprising value given how it behaves for all other inputs
+test("given an array with only non-number values, returns 0", () => {
+  expect(sum(["apple", null, undefined, "banana"])).toBe(0);
+});

From d95006e8ee6a01e87be02842ae613535910f1da5 Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Mon, 23 Mar 2026 17:44:02 +0000
Subject: [PATCH 12/13] Remove Sprint-1 files from Sprint-2 PR

---
 Sprint-1/fix/median.js            | 27 +++------------------------
 Sprint-1/implement/dedupe.js      | 18 +-----------------
 Sprint-1/implement/dedupe.test.js | 24 ++----------------------
 Sprint-1/implement/max.js         | 12 ------------
 Sprint-1/implement/max.test.js    | 23 ++---------------------
 Sprint-1/implement/sum.js         | 12 ------------
 Sprint-1/implement/sum.test.js    | 19 +------------------
 7 files changed, 9 insertions(+), 126 deletions(-)

diff --git a/Sprint-1/fix/median.js b/Sprint-1/fix/median.js
index 01b74c403..b22590bc6 100644
--- a/Sprint-1/fix/median.js
+++ b/Sprint-1/fix/median.js
@@ -6,30 +6,9 @@
 // or 'list' has mixed values (the function is expected to sort only numbers).
 
 function calculateMedian(list) {
-  // Return null immediately if the input is not an array
-  if (!Array.isArray(list)) {
-    return null;
-  }
-
-  // filter() returns a new array, so this does not modify the original input
-  const numbersOnly = list.filter((item) => Number.isFinite(item));
-
-  // Return null if there are no numeric values
-  if (numbersOnly.length === 0) {
-    return null;
-  }
-
-  // Safe to sort directly because numbersOnly is already a new array
-  const sortedNumbers = numbersOnly.sort((a, b) => a - b);
-  const middleIndex = Math.floor(sortedNumbers.length / 2);
-
-  // Even number of values: return the average of the two middle values
-  if (sortedNumbers.length % 2 === 0) {
-    return (sortedNumbers[middleIndex - 1] + sortedNumbers[middleIndex]) / 2;
-  }
-
-  // Odd number of values: return the middle value
-  return sortedNumbers[middleIndex];
+  const middleIndex = Math.floor(list.length / 2);
+  const median = list.splice(middleIndex, 1)[0];
+  return median;
 }
 
 module.exports = calculateMedian;
diff --git a/Sprint-1/implement/dedupe.js b/Sprint-1/implement/dedupe.js
index f8494b4a5..781e8718a 100644
--- a/Sprint-1/implement/dedupe.js
+++ b/Sprint-1/implement/dedupe.js
@@ -1,17 +1 @@
-// Return a new array with duplicate values removed.
-// Keep the first occurrence of each value.
-
-function dedupe(elements) {
-  const uniqueElements = [];
-
-  for (const element of elements) {
-    // Add the element only if it is not already in the result array
-    if (!uniqueElements.includes(element)) {
-      uniqueElements.push(element);
-    }
-  }
-
-  return uniqueElements;
-}
-
-module.exports = dedupe;
+function dedupe() {}
diff --git a/Sprint-1/implement/dedupe.test.js b/Sprint-1/implement/dedupe.test.js
index f4336cc48..23e0f8638 100644
--- a/Sprint-1/implement/dedupe.test.js
+++ b/Sprint-1/implement/dedupe.test.js
@@ -2,7 +2,7 @@ const dedupe = require("./dedupe.js");
 /*
 Dedupe Array
 
- Dedupe means deduplicate
+📖 Dedupe means **deduplicate**
 
 In this kata, you will need to deduplicate the elements of an array
 
@@ -16,32 +16,12 @@ E.g. dedupe([1, 2, 1]) target output: [1, 2]
 // Given an empty array
 // When passed to the dedupe function
 // Then it should return an empty array
-test("given an empty array, it returns an empty array", () => {
-  expect(dedupe([])).toEqual([]);
-});
+test.todo("given an empty array, it returns an empty array");
 
 // Given an array with no duplicates
 // When passed to the dedupe function
 // Then it should return a copy of the original array
-test("given an array with no duplicates, it returns a copy of the original array", () => {
-  const input = [1, 2, 3];
-  const result = dedupe(input);
-
-  expect(result).toEqual(input);
-  expect(result).not.toBe(input);
-});
 
 // Given an array with strings or numbers
 // When passed to the dedupe function
 // Then it should remove the duplicate values, preserving the first occurence of each element
-test("given an array with duplicate strings, removes duplicates and preserves first occurrence", () => {
-  expect(dedupe(["a", "a", "a", "b", "b", "c"])).toEqual(["a", "b", "c"]);
-});
-
-test("given an array with duplicate numbers, removes duplicates and preserves first occurrence", () => {
-  expect(dedupe([5, 1, 1, 2, 3, 2, 5, 8])).toEqual([5, 1, 2, 3, 8]);
-});
-
-test("given a mixed duplicate order, removes duplicates and preserves first occurrence", () => {
-  expect(dedupe([1, 2, 1])).toEqual([1, 2]);
-});
diff --git a/Sprint-1/implement/max.js b/Sprint-1/implement/max.js
index b9017f0bf..6dd76378e 100644
--- a/Sprint-1/implement/max.js
+++ b/Sprint-1/implement/max.js
@@ -1,16 +1,4 @@
-// Find the largest numerical value in an array.
-// Non-number values should be ignored.
-
 function findMax(elements) {
-  let maxValue = -Infinity;
-
-  for (const element of elements) {
-    if (Number.isFinite(element) && element > maxValue) {
-      maxValue = element;
-    }
-  }
-
-  return maxValue;
 }
 
 module.exports = findMax;
diff --git a/Sprint-1/implement/max.test.js b/Sprint-1/implement/max.test.js
index ebb57b922..82f18fd88 100644
--- a/Sprint-1/implement/max.test.js
+++ b/Sprint-1/implement/max.test.js
@@ -15,48 +15,29 @@ const findMax = require("./max.js");
 // Given an empty array
 // When passed to the max function
 // Then it should return -Infinity
-test("given an empty array, returns -Infinity", () => {
-  expect(findMax([])).toBe(-Infinity);
-});
+// Delete this test.todo and replace it with a test.
+test.todo("given an empty array, returns -Infinity");
 
 // Given an array with one number
 // When passed to the max function
 // Then it should return that number
-test("given an array with one number, returns that number", () => {
-  expect(findMax([42])).toBe(42);
-});
 
 // Given an array with both positive and negative numbers
 // When passed to the max function
 // Then it should return the largest number overall
-test("given an array with positive and negative numbers, returns the largest number", () => {
-  expect(findMax([-10, 3, 25, -1])).toBe(25);
-});
 
 // Given an array with just negative numbers
 // When passed to the max function
 // Then it should return the closest one to zero
-test("given an array with only negative numbers, returns the largest one", () => {
-  expect(findMax([-9, -2, -15, -4])).toBe(-2);
-});
 
 // Given an array with decimal numbers
 // When passed to the max function
 // Then it should return the largest decimal number
-test("given an array with decimal numbers, returns the largest decimal", () => {
-  expect(findMax([1.2, 3.8, 2.4])).toBe(3.8);
-});
 
 // Given an array with non-number values
 // When passed to the max function
 // Then it should return the max and ignore non-numeric values
-test("given an array with non-number values, ignores them and returns the max", () => {
-  expect(findMax(["hey", 10, "300", "hi", 60, 10])).toBe(60);
-});
 
 // Given an array with only non-number values
 // When passed to the max function
 // Then it should return the least surprising value given how it behaves for all other inputs
-test("given an array with only non-number values, returns -Infinity", () => {
-  expect(findMax(["apple", null, undefined, "banana"])).toBe(-Infinity);
-});
diff --git a/Sprint-1/implement/sum.js b/Sprint-1/implement/sum.js
index 59f5ecc83..9062aafe3 100644
--- a/Sprint-1/implement/sum.js
+++ b/Sprint-1/implement/sum.js
@@ -1,16 +1,4 @@
-// Sum the numerical values in an array.
-// Non-number values should be ignored.
-
 function sum(elements) {
-  let total = 0;
-
-  for (const element of elements) {
-    if (Number.isFinite(element)) {
-      total += element;
-    }
-  }
-
-  return total;
 }
 
 module.exports = sum;
diff --git a/Sprint-1/implement/sum.test.js b/Sprint-1/implement/sum.test.js
index 0698757ef..dd0a090ca 100644
--- a/Sprint-1/implement/sum.test.js
+++ b/Sprint-1/implement/sum.test.js
@@ -13,41 +13,24 @@ const sum = require("./sum.js");
 // Given an empty array
 // When passed to the sum function
 // Then it should return 0
-test("given an empty array, returns 0", () => {
-  expect(sum([])).toBe(0);
-});
+test.todo("given an empty array, returns 0")
 
 // Given an array with just one number
 // When passed to the sum function
 // Then it should return that number
-test("given an array with one number, returns that number", () => {
-  expect(sum([7])).toBe(7);
-});
 
 // Given an array containing negative numbers
 // When passed to the sum function
 // Then it should still return the correct total sum
-test("given an array with negative numbers, returns the correct sum", () => {
-  expect(sum([-5, 10, -2])).toBe(3);
-});
 
 // Given an array with decimal/float numbers
 // When passed to the sum function
 // Then it should return the correct total sum
-test("given an array with decimal numbers, returns the correct sum", () => {
-  expect(sum([1.2, 0.6, 0.005])).toBeCloseTo(1.805, 10);
-});
 
 // Given an array containing non-number values
 // When passed to the sum function
 // Then it should ignore the non-numerical values and return the sum of the numerical elements
-test("given an array with non-number values, ignores them and sums only numbers", () => {
-  expect(sum(["hey", 10, "hi", 60, 10])).toBe(80);
-});
 
 // Given an array with only non-number values
 // When passed to the sum function
 // Then it should return the least surprising value given how it behaves for all other inputs
-test("given an array with only non-number values, returns 0", () => {
-  expect(sum(["apple", null, undefined, "banana"])).toBe(0);
-});

From 4b01ab03bcd0cfdfc9ba93c21799c2e2d23d2a7f Mon Sep 17 00:00:00 2001
From: Richard Frimpong <richardfrimpongalx@gmail.com>
Date: Tue, 24 Mar 2026 01:23:50 +0000
Subject: [PATCH 13/13] Apply mentor feedback to Sprint 2 files

---
 Sprint-2/debug/recipe.js               |  6 ++--
 Sprint-2/implement/contains.js         | 19 ++++--------
 Sprint-2/implement/contains.test.js    | 26 ++++++++++++----
 Sprint-2/implement/querystring.js      | 39 +++++++++++++----------
 Sprint-2/implement/querystring.test.js |  6 ++++
 Sprint-2/implement/tally.js            | 11 +++----
 Sprint-2/implement/tally.test.js       |  6 ++++
 Sprint-2/stretch/count-words.js        | 43 +++++++++++++++++++++-----
 8 files changed, 103 insertions(+), 53 deletions(-)

diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 7b43deb42..42d351b6d 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -15,7 +15,5 @@ const recipe = {
 console.log(`${recipe.title} serves ${recipe.serves}`);
 console.log("ingredients:");
 
-// Loop through the ingredients array and print each one
-for (const ingredient of recipe.ingredients) {
-  console.log(ingredient);
-}
+// Print each ingredient on a new line using join()
+console.log(recipe.ingredients.join("\n"));
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index 1527711b2..c2b4995bf 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,27 +1,20 @@
 /**
  * contains()
  *
- * Checks whether an object contains a specific property.
+ * Checks whether an object contains a specific own property.
  *
  * @param {object} obj - The object to check.
- * @param {string} propertyName - The property name we want to check.
- * @returns {boolean} True if the property exists, otherwise false.
+ * @param {*} propertyName - The property name to check.
+ * @returns {boolean} True if the object has the property as its own key, otherwise false.
  */
-
 function contains(obj, propertyName) {
-  // Validate that obj is actually an object
-  // and not null or an array
+  // Reject null, non-objects, and arrays
   if (obj === null || typeof obj !== "object" || Array.isArray(obj)) {
     return false;
   }
 
-  // Validate propertyName
-  if (typeof propertyName !== "string" || propertyName.length === 0) {
-    return false;
-  }
-
-  // Check if the object has the property as its own key
-  return Object.prototype.hasOwnProperty.call(obj, propertyName);
+  // Check own properties only
+  return Object.hasOwn(obj, propertyName);
 }
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 67bbc115f..40bc1f961 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -1,11 +1,11 @@
 const contains = require("./contains.js");
 
 /*
-Implement a function called contains that checks an object contains a
-particular property
+Implement a function called contains that checks whether an object contains
+a particular own property.
 
-E.g. contains({a: 1, b: 2}, "a") // returns true
-E.g. contains({a: 1, b: 2}, "c") // returns false
+E.g. contains({ a: 1, b: 2 }, "a") // returns true
+E.g. contains({ a: 1, b: 2 }, "c") // returns false
 */
 
 describe("contains()", () => {
@@ -21,11 +21,25 @@ describe("contains()", () => {
     expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
   });
 
-  test("returns false when given an array", () => {
-    expect(contains(["a", "b"], "0")).toBe(false);
+  test("returns false for inherited properties", () => {
+    expect(contains({ a: 1, b: 2 }, "toString")).toBe(false);
+  });
+
+  test("returns false when given an array with a realistic array key", () => {
+    expect(contains(["a", "b"], 0)).toBe(false);
   });
 
   test("returns false when given null", () => {
     expect(contains(null, "a")).toBe(false);
   });
+
+  test("supports non-string property names", () => {
+    const obj = { 3: 12 };
+    expect(contains(obj, 3)).toBe(true);
+  });
+
+  test("supports empty string as a property name", () => {
+    const obj = { "": 99 };
+    expect(contains(obj, "")).toBe(true);
+  });
 });
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 617ea20e3..314f95121 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,42 +1,49 @@
 /**
  * parseQueryString()
  *
- * Parses a query string into an object of key-value pairs.
+ * Parses a query string into an object of decoded key-value pairs.
  *
- * Example:
- * parseQueryString("name=Richard&city=Sheffield")
- * returns { name: "Richard", city: "Sheffield" }
+ * Handles:
+ * - empty strings
+ * - multiple pairs separated by "&"
+ * - values containing "="
+ * - missing values
+ * - missing "="
+ * - trailing "&"
+ * - URL-encoded keys and values
  */
-
 function parseQueryString(queryString) {
-  const queryParams = {};
+  const queryParams = Object.create(null);
 
-  // Return an empty object if the input is an empty string
+  // Return an empty object if the input is invalid or empty
   if (typeof queryString !== "string" || queryString.length === 0) {
     return queryParams;
   }
 
-  // Split the full query string into key-value pairs
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    // Skip empty pairs, for example from a trailing "&"
+    // Skip empty pairs, e.g. from a trailing "&"
     if (pair === "") {
       continue;
     }
 
-    // Find the position of the first "="
     const separatorIndex = pair.indexOf("=");
 
-    // If there is no "=" sign, treat it as a key with an empty value
+    let rawKey;
+    let rawValue;
+
+    // If there is no "=", treat it as a key with an empty value
     if (separatorIndex === -1) {
-      queryParams[pair] = "";
-      continue;
+      rawKey = pair;
+      rawValue = "";
+    } else {
+      rawKey = pair.slice(0, separatorIndex);
+      rawValue = pair.slice(separatorIndex + 1);
     }
 
-    // Extract the key and everything after the first "=" as the value
-    const key = pair.slice(0, separatorIndex);
-    const value = pair.slice(separatorIndex + 1);
+    const key = decodeURIComponent(rawKey);
+    const value = decodeURIComponent(rawValue);
 
     queryParams[key] = value;
   }
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 431d6fd13..d095e470c 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -41,4 +41,10 @@ describe("parseQueryString()", () => {
       name: "Richard",
     });
   });
+
+  test("decodes URL-encoded keys and values", () => {
+    expect(parseQueryString("tags%5B%5D=hello%20world")).toEqual({
+      "tags[]": "hello world",
+    });
+  });
 });
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index d6ee073a8..2e1df259c 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -4,25 +4,22 @@
  * Counts how many times each item appears in an array.
  *
  * Example:
- * tally(['a','a','b','c'])
+ * tally(["a", "a", "b", "c"])
  * returns { a: 2, b: 1, c: 1 }
  */
-
 function tally(items) {
   // Validate input
   if (!Array.isArray(items)) {
     throw new Error("Expected an array");
   }
 
-  const counts = {};
+  // Create an object with no inherited properties
+  const counts = Object.create(null);
 
-  // Loop through each item in the array
   for (const item of items) {
-    // If the item already exists in the object, increase the count
-    if (counts[item]) {
+    if (counts[item] !== undefined) {
       counts[item] += 1;
     } else {
-      // Otherwise initialise it
       counts[item] = 1;
     }
   }
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 6d80fc996..78d533547 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -24,4 +24,10 @@ describe("tally()", () => {
   test("throws an error for invalid input", () => {
     expect(() => tally("not-an-array")).toThrow();
   });
+
+  test('counts inherited-looking keys like "toString" correctly', () => {
+    expect(tally(["toString", "toString"])).toEqual({
+      toString: 2,
+    });
+  });
 });
diff --git a/Sprint-2/stretch/count-words.js b/Sprint-2/stretch/count-words.js
index dbea38d13..fdb0b3d58 100644
--- a/Sprint-2/stretch/count-words.js
+++ b/Sprint-2/stretch/count-words.js
@@ -1,20 +1,49 @@
+/*
+  Count the number of times a word appears in a given string.
+
+  Write a function called countWords that:
+    - takes a string as an argument
+    - returns an object where:
+        - the keys are the words from the string
+        - the values are the number of times each word appears
+
+  Example:
+  countWords("you and me and you")
+  returns { you: 2, and: 2, me: 1 }
+
+  Advanced improvements included:
+    - removes punctuation
+    - ignores case
+    - handles extra whitespace
+    - safely counts words like "constructor"
+*/
+
 function countWords(text) {
+  // Validate input
   if (typeof text !== "string") {
     throw new Error("Input must be a string");
   }
 
-  // remove punctuation and make lowercase
-  const cleanedText = text.toLowerCase().replace(/[.,!?]/g, "");
+  // Convert to lowercase, replace punctuation with spaces, and trim edges
+  const cleanedText = text
+    .toLowerCase()
+    .replace(/[.,!?;:]/g, " ")
+    .trim();
 
+  // Return an empty object if nothing remains after cleaning
+  if (cleanedText === "") {
+    return Object.create(null);
+  }
+
+  // Split on one or more whitespace characters
   const words = cleanedText.split(/\s+/);
 
-  const counts = {};
+  // Use an object with no inherited properties
+  const counts = Object.create(null);
 
   for (const word of words) {
-    if (!word) continue;
-
-    if (counts[word]) {
-      counts[word]++;
+    if (counts[word] !== undefined) {
+      counts[word] += 1;
     } else {
       counts[word] = 1;
     }