preCourse1 assignment

Exercise_1.java

@@ -1,40 +1,56 @@
-class Stack { 
+/*
+ Time complexity isEmpty => O(1), push => O(1), pop => O(1)
+ */
+
+
+class Stack {
     //Please read sample.java file before starting.
   //Kindly include Time and Space complexity at top of each file
     static final int MAX = 1000; 
-    int top; 
+    int top;
+    int size = 0;
     int a[] = new int[MAX]; // Maximum size of Stack 
 
     boolean isEmpty() 
     { 
-        //Write your code here 
+        return top == 0;
     } 
 
     Stack() 
     { 
-        //Initialize your constructor 
+        top = 0 ;
+        size = 0;
     } 
 
     boolean push(int x) 
-    { 
-        //Check for stack Overflow
-        //Write your code here
+    {
+        if (top >= MAX -1) {
+            System.out.println("Stack Overflow");
+            return false;
+        }
+        a[top++] = x;
+        return true;
     } 
 
     int pop() 
     { 
         //If empty return 0 and print " Stack Underflow"
         //Write your code here
+        if(top == 0) {
+            print(" Stack Underflow");
+            return 0;
+        }
+        return a[top--];
     } 
 
     int peek() 
-    { 
-        //Write your code here
+    {
+        return a[top];
     } 
 } 
 
 // Driver code 
-class Main { 
+public  class Exercise_1 {
     public static void main(String args[]) 
     { 
         Stack s = new Stack(); 

Exercise_2.java

@@ -8,31 +8,56 @@ static class StackNode {
 
         StackNode(int data) 
         { 
-            //Constructor here 
+            StackNode node = new StackNode();
+            node.data = data;
+            node.next = null;
         } 
     } 
 
 
     public boolean isEmpty() 
     { 
-        //Write your code here for the condition if stack is empty. 
+        return root == null ;
     } 
 
     public void push(int data) 
     { 
-        //Write code to push data to the stack. 
+        StackNode node = new StackNode(data);
+
+        if (root == null) {
+            root = node;
+        }
+        else {
+            node.next = root;
+            root = node;
+        }
     } 
 
     public int pop() 
-    { 	
+    {
 	//If Stack Empty Return 0 and print "Stack Underflow"
         //Write code to pop the topmost element of stack.
-	//Also return the popped element 
+	//Also return the popped element
+        if( root == null) {
+            System.out.println("Stack Underflow");
+            return  0;
+        }
+        else {
+            int val = root.data;
+            root = root.next;
+            return val;
+        }
     } 
 
     public int peek() 
     { 
         //Write code to just return the topmost element without removing it.
+        if (root == null) {
+            return 0;
+        }
+        else {
+            return root.data;
+        }
     } 
 
 	//Driver code

Exercise_3.java

@@ -1,7 +1,7 @@
 import java.io.*; 
 
-// Java program to implement 
-// a Singly Linked List 
+// Time complexity: insert => O(n) where n is the size of the elements
+// Space complexity: insert => O(1)
 public class LinkedList { 
 
     Node head; // head of list 
@@ -17,24 +17,36 @@ static class Node {
         // Constructor 
         Node(int d) 
         { 
-            //Write your code here 
+            //Write your code here
+            Node a = new Node();
+            a.data = d;
+            a.next = null;
+
         } 
     } 
 
     // Method to insert a new node 
     public static LinkedList insert(LinkedList list, int data) 
     { 
         // Create a new node with given data 
-
+        Node a = new Node(data);
+
+
+
         // If the Linked List is empty, 
         // then make the new node as head 
-
-            // Else traverse till the last node 
-            // and insert the new_node there 
+        if(list == null) {
+            head = a;
+        }
+        else {
+            Node curr = head;
 
-            // Insert the new_node at last node 
-        // Return the list by head 
-
+            while (curr.next != null) {
+                curr = curr.next;
+            }
+            curr.next = a;
+            return  head;
+        }
     } 
 
     // Method to print the LinkedList.