PreCourse-1 Complete

Exercise_1.java

@@ -1,3 +1,5 @@
+// Time Complexity: O(1) for all operations
+// Space Complexity: O(n) //n=size of Stack
 class Stack { 
     //Please read sample.java file before starting.
   //Kindly include Time and Space complexity at top of each file
@@ -8,28 +10,53 @@ class Stack {
     boolean isEmpty() 
     { 
         //Write your code here 
+        if(top==-1)
+     {   return true;}
+
+        return false;
+
     } 
 
     Stack() 
     { 
         //Initialize your constructor 
+        top=-1;
     } 
 
     boolean push(int x) 
     { 
         //Check for stack Overflow
         //Write your code here
+        if(top==MAX-1){
+            System.out.println("Stack Overflow");
+            return false;
+        }else
+        {top++;
+        a[top]=x;
+        return true;}
     } 
 
     int pop() 
     { 
         //If empty return 0 and print " Stack Underflow"
-        //Write your code here
+        if(top==-1){
+            System.out.println("Stack Underflow");
+            return 0;
+
+        }else{
+            int m=a[top];
+            top--;
+            return m;
+        }
     } 
 
     int peek() 
     { 
         //Write your code here
+        if(top==-1){
+            return -1;
+        }
+        return a[top];
     } 
 } 
 

LinkedList.java

@@ -0,0 +1,91 @@
+import java.io.*; 
+//Time Complexity : O(n)
+//Space Complexity : O(n)
+
+// Java program to implement 
+// a Singly Linked List 
+public class LinkedList { 
+
+    Node head; // head of list 
+
+    // Linked list Node. 
+    // This inner class is made static 
+    // so that main() can access it 
+    static class Node { 
+
+        int data; 
+        Node next; 
+
+        // Constructor 
+        Node(int d) 
+        { 
+            //Write your code here 
+            this.data=d;
+            this.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, 
+        // then make the new node as head 
+        if(list.head==null){
+            list.head=newNode;
+        }else{
+            // Else traverse till the last node 
+            // and insert the new_node there 
+            Node temp=list.head;
+            while(temp.next!=null){
+                temp=temp.next;
+            }
+            // Insert the new_node at last node 
+            temp.next=newNode;
+        }
+
+        // Return the list by head 
+        return list;
+    } 
+
+    // Method to print the LinkedList. 
+    public static void printList(LinkedList list) 
+    {  
+        // Traverse through the LinkedList 
+        Node cNode=list.head;
+        while(cNode!=null){
+            // Print the data at current node 
+            System.out.print(cNode.data + " ");
+            // Go to next node 
+            cNode=cNode.next;
+        }
+
+
+
+
+    } 
+
+    // Driver code 
+    public static void main(String[] args) 
+    { 
+        /* Start with the empty list. */
+        LinkedList list = new LinkedList(); 
+
+        // 
+        // ******INSERTION****** 
+        // 
+
+        // Insert the values 
+        list = insert(list, 1); 
+        list = insert(list, 2); 
+        list = insert(list, 3); 
+        list = insert(list, 4); 
+        list = insert(list, 5); 
+
+        // Print the LinkedList 
+        printList(list); 
+    } 
+}

StackAsLinkedList.java

@@ -0,0 +1,86 @@
+//Time Complexity:  O(1)
+//Space Complexity: O(n)
+
+public class StackAsLinkedList { 
+
+    StackNode root; 
+
+    static class StackNode { 
+        int data; 
+        StackNode next; 
+
+        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;
+
+        return false;
+
+    } 
+
+    public void push(int data) 
+    { 
+        //Write code to push data to the stack. 
+        StackNode newnode=new StackNode(data);
+        if(root == null){
+            root=newnode;
+        }else{
+            StackNode temp=root;
+            root=newnode;
+            newnode.next=temp;
+
+        }
+
+    } 
+
+    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(isEmpty()){
+        System.out.print("Stack Underflow");
+        return 0;
+
+    }
+    int popped=root.data;
+    root=root.next;
+    return popped;
+    } 
+
+    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
+    public static void main(String[] args) 
+    { 
+
+        StackAsLinkedList sll = new StackAsLinkedList(); 
+
+        sll.push(10); 
+        sll.push(20); 
+        sll.push(30); 
+
+        System.out.println(sll.pop() + " popped from stack"); 
+
+        System.out.println("Top element is " + sll.peek()); 
+    } 
+}