Done PreCourse-1

Exercise_1.java

@@ -1,3 +1,6 @@
+// Time complexity O(1) for each operation
+// Problems faced: Unable to calculate the time and spce complexity properly
+
 class Stack { 
     //Please read sample.java file before starting.
   //Kindly include Time and Space complexity at top of each file
@@ -7,29 +10,55 @@ class Stack {
 
     boolean isEmpty() 
     { 
-        //Write your code here 
+        if(top==-1)
+            return true;
+        else
+            return false;
     } 
 
     Stack() 
     { 
         //Initialize your constructor 
+        top=-1;
     } 
 
     boolean push(int x) 
     { 
         //Check for stack Overflow
+        if(top>MAX-1)
+            return false;
+        else
+        {
+            top=top+1;
+            a[top]=x;
+            return true;
+        }
         //Write your code here
     } 
 
     int pop() 
     { 
         //If empty return 0 and print " Stack Underflow"
+        if(top==-1)
+        {
+            System.out.print("Stack Underflow");
+            return 0;
+        }
+        else
+            return a[top--];
         //Write your code here
     } 
 
     int peek() 
     { 
         //Write your code here
+        if(top==-1)
+        {
+            System.out.println("Stack is empty");
+            return 0;
+        }
+        else
+            return a[top];
     } 
 } 
 
@@ -42,5 +71,6 @@ public static void main(String args[])
         s.push(20); 
         s.push(30); 
         System.out.println(s.pop() + " Popped from stack"); 
+
     } 
 }

Exercise_3.java → LinkedList.java

@@ -18,16 +18,34 @@ static class Node {
         Node(int d) 
         { 
             //Write your code here 
+            this.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 
+        // then make the new node as head
+        if(list.head==null)
+        {
+            list.head=newNode;
+        }
+        else
+        {
+            Node temp =list.head;
+            while(temp.next!= null)
+            {
+                temp=temp.next;
+            }
+            temp.next=newNode;
+        } 
+        return list;
 
             // Else traverse till the last node 
             // and insert the new_node there 
@@ -41,7 +59,12 @@ public static LinkedList insert(LinkedList list, int data)
     public static void printList(LinkedList list) 
     {  
         // Traverse through the LinkedList 
-
+        Node temp=list.head;
+        while(temp !=null)
+        {
+            System.out.println(temp.data+ " ");
+            temp=temp.next;
+        }
             // Print the data at current node 
 
             // Go to next node 

Exercise_2.java → StackAsLinkedList.java

@@ -8,6 +8,8 @@ static class StackNode {
 
         StackNode(int data) 
         { 
+            this.data=data;
+            this.next=null;
             //Constructor here 
         } 
     } 
@@ -16,23 +18,59 @@ static class StackNode {
     public boolean isEmpty() 
     { 
         //Write your code here for the condition if stack is empty. 
+
+        if(root==null)
+            return true;
+        return false;
     } 
 
     public void push(int data) 
     { 
-        //Write code to push data to the stack. 
+        //Write code to push data to the stack.
+        StackNode newNode=new StackNode(data) ;
+        if(root==null)
+        {
+            root=newNode;
+            newNode.next=null;
+        }
+        else{
+            newNode.next=root;
+            root=newNode;
+        }
     } 
 
     public int pop() 
     { 	
 	//If Stack Empty Return 0 and print "Stack Underflow"
+        if(root==null)
+        {
+            System.out.println("Stack Underflow");
+            return 0;
+        }
+        else{
+            StackNode temp =root;
+            int x=temp.data;
+            root=temp.next;
+            temp=null;
+            return x;
+        }
         //Write code to pop the topmost element of stack.
 	//Also return the popped element 
     } 
 
     public int peek() 
     { 
         //Write code to just return the topmost element without removing it.
+        if(root==null)
+        {
+            System.out.println("Stack is empty");
+            return 0;
+        }
+        else
+        {
+        StackNode temp= root;
+        return temp.data;
+        }
     } 
 
 	//Driver code