Done precourse1

Exercise_1.java

@@ -7,29 +7,45 @@ class Stack {
 
     boolean isEmpty() 
     { 
-        //Write your code here 
+        return top == -1;
     } 
 
     Stack() 
     { 
-        //Initialize your constructor 
+        this.top = -1;
     } 
 
     boolean push(int x) 
     { 
-        //Check for stack Overflow
-        //Write your code here
+        if(top == MAX -1) {
+            throw new RuntimeException("Stack Overflow has occurred");
+        }
+        else{
+            a[++top]=x;
+            return true;
+        }
     } 
 
     int pop() 
     { 
-        //If empty return 0 and print " Stack Underflow"
-        //Write your code here
+        if(top ==-1)
+        {
+            throw new RuntimeException("Stack Underflow has occurred");
+        }
+        else {
+            return a[top--];
+        }
     } 
 
     int peek() 
-    { 
-        //Write your code here
+    {
+        if(top ==-1)
+        {
+            throw new RuntimeException("Stack Underflow has occurred");
+        }
+        else {
+            return a[top];
+        }
     } 
 } 
 

Exercise_2.java

@@ -1,4 +1,4 @@
-public class StackAsLinkedList { 
+class StackAsLinkedList {
 
     StackNode root; 
 
@@ -8,31 +8,46 @@ static class StackNode {
 
         StackNode(int data) 
         { 
-            //Constructor here 
-        } 
+           this.data =data;
+           this.next =next;
+        }
     } 
-    
+
 
     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);
+        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 
+    {
+        if(root == null)
+        {
+            throw new RuntimeException("Stack Underflow has occurred");
+        }
+        else {
+	        int data = root.data;
+            root = root.next;
+            return data;
+     }
     } 
 
     public int peek() 
-    { 
-        //Write code to just return the topmost element without removing it.
+    {
+        if(root == null)
+        {
+            throw new RuntimeException("Stack Underflow has occurred");
+        }
+        else{
+            return root.data;
+        }
     } 
 
 	//Driver code

Exercise_3.java

@@ -2,7 +2,7 @@
 
 // Java program to implement 
 // a Singly Linked List 
-public class LinkedList { 
+class LinkedList {
 
     Node head; // head of list 
 
@@ -17,34 +17,39 @@ static class Node {
         // Constructor 
         Node(int d) 
         { 
-            //Write your code here 
+            data =d;
         } 
     } 
 
     // Method to insert a new node 
     public static LinkedList insert(LinkedList list, int data) 
     { 
-        // Create a new node with given data 
+        Node newNode = 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.head == null){
+           list.head = newNode;
+       }
+       else {
+           Node lastNode = list.head;
+           while(lastNode.next !=null){
+               lastNode = lastNode.next;
+           }
+           lastNode.next = newNode;
+       }
 
-            // Insert the new_node at last node 
-        // Return the list by head 
+        return list;
 
     } 
 
     // Method to print the LinkedList. 
     public static void printList(LinkedList list) 
     {  
-        // Traverse through the LinkedList 
-
-            // Print the data at current node 
-
-            // Go to next node 
+        Node currentNode = list.head;
+
+        while (currentNode != null){
+            System.out.print(currentNode.data + " ");
+            currentNode = currentNode.next;
+    }
     } 
 
     // Driver code