Precourse 1completed

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+  "java.debug.settings.onBuildFailureProceed": true
+}

Exercise_1.java

@@ -1,22 +1,43 @@
 class Stack { 
-    //Please read sample.java file before starting.
-  //Kindly include Time and Space complexity at top of each file
+
+  //Time Complexity:O(1) and Space Complexity:O(n)
     static final int MAX = 1000; 
     int top; 
     int a[] = new int[MAX]; // Maximum size of Stack 
 
     boolean isEmpty() 
     { 
         //Write your code here 
+        if(top==-1)
+        {
+            System.out.println("Stack is empty");
+            return true;
+        }
+        else{
+            System.out.println("Stack is not empty");
+            return false;
+        }
+
     } 
 
     Stack() 
     { 
+        top=-1;
         //Initialize your constructor 
     } 
 
     boolean push(int x) 
     { 
+        if(top==MAX-1)
+        {
+            System.out.println("Stack overflow");
+            return false;
+
+        }
+        else{
+            a[++top]=x;
+            return true;
+        }
         //Check for stack Overflow
         //Write your code here
     } 
@@ -25,10 +46,20 @@ int pop()
     { 
         //If empty return 0 and print " Stack Underflow"
         //Write your code here
+        if(isEmpty())
+        {
+            System.out.println("Stack underflow");
+            return 0;
+        }
+        else{
+            int x=a[top--];
+            return x;
+        }
     } 
 
     int peek() 
     { 
+        return a[top];
         //Write your code here
     } 
 } 
@@ -41,6 +72,8 @@ public static void main(String args[])
         s.push(10); 
         s.push(20); 
         s.push(30); 
+
         System.out.println(s.pop() + " Popped from stack"); 
+
     } 
 }

Exercise_3.java → LinkedList.java

@@ -1,70 +1,95 @@
-import java.io.*; 
-
-// 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 
-        } 
-    } 
-
-    // Method to insert a new node 
-    public static LinkedList insert(LinkedList list, int data) 
-    { 
-        // Create a new node with given 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 
-
-            // Insert the new_node at last node 
-        // Return the list by head 
-
-    } 
-
-    // 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 
-    } 
-
-    // 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); 
-    } 
+// a Singly Linked List 
+//Time and Space Complexity:O(n)
+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) 
+        {  this.data=d;
+           next=null;
+
+            //Write your code here 
+        } 
+    } 
+
+    // Method to insert a new node 
+    public static LinkedList insert(LinkedList list, int data) 
+    {   Node newNode=new Node(data);
+
+        if(list.head==null){
+
+            list.head=newNode;
+        }
+        else{
+            Node temp=list.head;
+            while(temp.next!=null)
+            {
+                temp=temp.next;
+            }
+            temp.next=newNode;
+
+        }
+        return list;
+        // Create a new node with given 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 
+
+            // Insert the new_node at last node 
+        // Return the list by head 
+
+    } 
+
+    // Method to print the LinkedList. 
+    public static void printList(LinkedList list) 
+    {  
+        // Traverse through the LinkedList 
+        if(list.head==null)
+        {
+            System.out.println("list is empty");
+        }
+        else{
+        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 
+    } 
+
+    // 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); 
+    } 
 }

Exercise_2.java → StackAsLinkedList.java

@@ -1,52 +1,79 @@
-public class StackAsLinkedList { 
-
-    StackNode root; 
-
-    static class StackNode { 
-        int data; 
-        StackNode next; 
-
-        StackNode(int data) 
-        { 
-            //Constructor here 
-        } 
-    } 
-
-
-    public boolean isEmpty() 
-    { 
-        //Write your code here for the condition if stack is empty. 
-    } 
-
-    public void push(int data) 
-    { 
-        //Write code to push data to the stack. 
-    } 
-
-    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 
-    } 
-
-    public int peek() 
-    { 
-        //Write code to just return the topmost element without removing it.
-    } 
-
-	//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()); 
-    } 
-} 
+//Complexity time O(1) Space O(n)
+public class StackAsLinkedList { 
+
+    StackNode root; 
+
+    static class StackNode { 
+        int data; 
+        StackNode next; 
+
+
+        StackNode(int data) 
+        { 
+            //Constructor here
+            this .data=data;
+            next=null;
+
+        } 
+    } 
+
+
+    public boolean isEmpty() 
+    {    if(root==null){
+        System.out.println("Stack is empty");
+        return true;
+    }
+    else{
+        System.out.println("Stack is not empty");
+        return false;
+    }
+        //Write your code here for the condition if stack is empty. 
+    } 
+
+    public void push(int data) 
+    {   StackNode newNode=new StackNode(data);
+        if(root==null){
+            root=newNode;
+        }
+        newNode.next=root;
+        root=newNode;
+
+        //Write code to push data to the stack. 
+    } 
+
+    public int pop() 
+    { 	
+        if(root==null){
+            System.out.println("Stack underflow");
+            return 0;
+        }
+        else{
+            int x=root.data;
+            root=root.next;
+            return x;
+        }
+	//If Stack Empty Return 0 and print "Stack Underflow"
+        //Write code to pop the topmost element of stack.
+	//Also return the popped element 
+    } 
+
+    public int peek() 
+    {   return root.data;
+        //Write code to just return the topmost element without removing it.
+    } 
+
+	//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()); 
+    } 
+}