From 8d05fa14333a42d451d2d36b600c6c5a4b3459c2 Mon Sep 17 00:00:00 2001
From: Vishal kumar M G <vishalkumarmg@Vishals-MBP-2.lan>
Date: Tue, 2 Jun 2026 20:59:53 -0500
Subject: [PATCH] PreCourse 1 complete

---
 Exercise_1.py | 13 +++++++++----
 Exercise_2.py |  9 +++++++++
 Exercise_3.py | 30 +++++++++++++++++++++++++++++-
 3 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/Exercise_1.py b/Exercise_1.py
index 532833f5d..57dea2d1b 100644
--- a/Exercise_1.py
+++ b/Exercise_1.py
@@ -2,20 +2,25 @@ class myStack:
   #Please read sample.java file before starting.
   #Kindly include Time and Space complexity at top of each file
      def __init__(self):
+          self.stack = []
          
      def isEmpty(self):
+          return self.stack == []
          
      def push(self, item):
+          self.stack.append(item)
          
      def pop(self):
-        
+          return self.stack.pop()
         
      def peek(self):
-        
+          return self.stack[-1]
+     
      def size(self):
-         
+          return len(self.stack)
+     
      def show(self):
-         
+          return self.stack
 
 s = myStack()
 s.push('1')
diff --git a/Exercise_2.py b/Exercise_2.py
index b11492215..ead479ade 100644
--- a/Exercise_2.py
+++ b/Exercise_2.py
@@ -6,10 +6,19 @@ def __init__(self, data):
  
 class Stack:
     def __init__(self):
+        self.stack = Node(None)
         
     def push(self, data):
+        new_node = Node(data)
+        new_node.next = self.stack
+        self.stack = new_node
         
     def pop(self):
+        if self.stack.data is None:
+            return None
+        popped_data = self.stack.data
+        self.stack = self.stack.next
+        return popped_data
         
 a_stack = Stack()
 while True:
diff --git a/Exercise_3.py b/Exercise_3.py
index a5d466b59..fef0bd935 100644
--- a/Exercise_3.py
+++ b/Exercise_3.py
@@ -3,6 +3,8 @@ class ListNode:
     A node in a singly-linked list.
     """
     def __init__(self, data=None, next=None):
+        self.data = data
+        self.next = next
     
 class SinglyLinkedList:
     def __init__(self):
@@ -10,6 +12,7 @@ def __init__(self):
         Create a new singly-linked list.
         Takes O(1) time.
         """
+        self.node = ListNode()
         self.head = None
 
     def append(self, data):
@@ -17,16 +20,41 @@ def append(self, data):
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
-        
+        new_node = ListNode(data)
+        if not self.head:
+            self.head = new_node
+        else:
+            current = self.head
+            while current.next:
+                current = current.next
+            current.next = new_node
+
     def find(self, key):
         """
         Search for the first element with `data` matching
         `key`. Return the element or `None` if not found.
         Takes O(n) time.
         """
+        current = self.head
+        while current:
+            if current.data == key:
+                return current
+            current = current.next
+        return None
         
     def remove(self, key):
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+        current = self.head
+        previous = None
+        while current:
+            if current.data == key:
+                if previous:
+                    previous.next = current.next
+                else:
+                    self.head = current.next
+                return
+            previous = current
+            current = current.next
\ No newline at end of file