Completed precourse-1

Exercise_1.java

@@ -1,5 +1,7 @@
 class Stack { 
     //Please read sample.java file before starting.
+    //Time Complexity: 0(1)
+    //Space Complexity: 0(n)
   //Kindly include Time and Space complexity at top of each file
     static final int MAX = 1000; 
     int top; 
@@ -8,28 +10,55 @@ class Stack {
     boolean isEmpty() 
     { 
         //Write your code here 
+        if(top<0){
+            return true;
+            else{
+                return false;
+            }
+        }
     } 
 
     Stack() 
     { 
         //Initialize your constructor 
+        top=-1;
     } 
 
     boolean push(int x) 
     { 
         //Check for stack Overflow
+        if(top>=Max-1)
+        {
+        System.out.println("stack Overflow");
+        return false;
+        }
         //Write your code here
+        top = top+1;
+        a[top]=x;
+        return true;
     } 
 
     int pop() 
     { 
         //If empty return 0 and print " Stack Underflow"
+        if(isEmpty()){
+            System.out.println("Stack Underflow")
+            return 0;
+        }
         //Write your code here
+        int value=a[top];
+        top=top-1;
+        return value;
     } 
 
     int peek() 
     { 
         //Write your code here
+        if(isEmpty()){
+            System.out.println("Stack is Empty");
+            return 0;
+        }
+        return a[top];
     } 
 } 
 

Exercise_2.java

@@ -1,3 +1,5 @@
+//Time Complexity: 0(1)
+//Space Complexity: 0(n)
 public class StackAsLinkedList { 
 
     StackNode root; 
@@ -9,30 +11,53 @@ static class StackNode {
         StackNode(int data) 
         { 
             //Constructor here 
+            this.data=data;
+            this.next=null;
         } 
     } 
 
 
     public boolean isEmpty() 
     { 
         //Write your code here for the condition if stack is empty. 
+        if(root==null){
+            return true;
+        }else{
+            return false;
+        }
     } 
 
     public void push(int data) 
     { 
         //Write code to push data to the stack. 
+        StackNode newNode =new StackNode(data);
+        newNode.next=root;
+        root=newNode;
+        System.out.println(data+"pushed to stack");
     } 
 
     public int pop() 
     { 	
 	//If Stack Empty Return 0 and print "Stack Underflow"
+    if(isEmpty()){
+        System.out.println("Stack Underflow");
+        return 0;
+    }
         //Write code to pop the topmost element of stack.
+        int poppedValue=root.data;
+        root=root.next;
+        return poppedValue;
 	//Also return the popped element 
     } 
 
     public int peek() 
     { 
         //Write code to just return the topmost element without removing it.
+        if(isEmpty()){
+            System.out.println("Stack is Empty");
+            return 0;
+        }
+        return root.data;
     } 
 
 	//Driver code

Exercise_3.java

@@ -18,33 +18,51 @@ static class Node {
         Node(int d) 
         { 
             //Write your code here 
+            data=d;
+            next=null;
         } 
     } 
 
     // 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, 
+        if(list.head==null){
+            list.head=newNode;
+        }
         // then make the new node as head 
-
             // Else traverse till the last node 
             // and insert the new_node there 
-
+            else{
+                Node last=list.head;
+                while (last.next!=null){
+                    last=last.next;
+                }
+
             // Insert the new_node at last node 
+            last.next=new_node;
+        }    
         // Return the list by head 
+        return list;
 
     } 
 
     // Method to print the LinkedList. 
     public static void printList(LinkedList list) 
     {  
         // Traverse through the LinkedList 
+        Node currentNode = list.head;
+        while(currentNode!=null){
+            System.out.print(currentNode.data+" ");
+        }
 
             // Print the data at current node 
 
             // Go to next node 
+            currentNode=currentNode.next;
     } 
 
     // Driver code