precourse 1 completed

Exercise_1.java

@@ -4,32 +4,56 @@ class Stack {
     static final int MAX = 1000; 
     int top; 
     int a[] = new int[MAX]; // Maximum size of Stack 
-
+  // Time Complexity :O(1)
+// Space Complexity :O(1)
     boolean isEmpty() 
     { 
         //Write your code here 
+        if(top==-1)
+            return true;
+
+        return false;
     } 
 
     Stack() 
     { 
         //Initialize your constructor 
+        top = -1;
     } 
-
+   // Time Complexity :O(1)
+// Space Complexity :O(N)
     boolean push(int x) 
     { 
         //Check for stack Overflow
+        if(top==MAX-1)
+            return false;
         //Write your code here
+        top++;
+        a[top] = x;
+        return true;
     } 
-
+   // Time Complexity :O(1)
+// Space Complexity :O(1)
     int pop() 
     { 
         //If empty return 0 and print " Stack Underflow"
+        if(top==-1){
+            System.out.println("Stack Underflow");
+        }
         //Write your code here
+        int val = a[top];
+        top--;
+        return val;
     } 
-
+   // Time Complexity :O(N)
+// Space Complexity :O(1)
     int peek() 
     { 
         //Write your code here
+        if(top==-1)
+            return -1;
+
+        return a[top];
     } 
 } 
 

Exercise_3.java → LinkedList.java

@@ -18,30 +18,49 @@ static class Node {
         Node(int d) 
         { 
             //Write your code here 
+            data = d;
+            this.next = null;
         } 
     } 
-
+   // Time Complexity :O(1)
+// Space Complexity :O(N)
     // Method to insert a new node 
     public static LinkedList insert(LinkedList list, int data) 
     { 
         // Create a new node with given data 
-
+        Node temp = new Node(data);
         // If the Linked List is empty, 
         // then make the new node as head 
-
+        if(list.head==null)
+        {
+            list.head = temp;
+        }
             // Else traverse till the last node 
+        else{
+            Node travel = list.head;
+            while(travel.next!=null){
+                travel = travel.next;
+            }
+            travel.next = temp;
+        }
             // and insert the new_node there 
 
             // Insert the new_node at last node 
         // Return the list by head 
-
+        return list;
     } 
 
     // Method to print the LinkedList. 
+     // Time Complexity :O(N)
+// Space Complexity :O(N)
     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

@@ -9,30 +9,58 @@ static class StackNode {
         StackNode(int data) 
         { 
             //Constructor here 
+            this.data = data;
+            this.next = null;
         } 
     } 
 
-
+	 // Time Complexity :O(1)
+// Space Complexity :O(1)
     public boolean isEmpty() 
     { 
         //Write your code here for the condition if stack is empty. 
+        if(root==null)
+            return true;
+
+        return false;
     } 
-
+   // Time Complexity :O(1)
+// Space Complexity :O(1)
     public void push(int data) 
     { 
         //Write code to push data to the stack. 
+        StackNode temp = new StackNode(data);
+        temp.next = root;
+        root = temp;
     } 
-
+   // Time Complexity :O(1)
+// Space Complexity :O(1)
     public int pop() 
     { 	
 	//If Stack Empty Return 0 and print "Stack Underflow"
+        if(root == null){
+            System.out.println("Stack Underflow");
+            return 0;
+        }
+
         //Write code to pop the topmost element of stack.
+        int val = root.data;
+        root = root.next;
+        return val;
+
 	//Also return the popped element 
     } 
-
+   // Time Complexity :O(1)
+// Space Complexity :O(1)
     public int peek() 
     { 
         //Write code to just return the topmost element without removing it.
+        if(root == null){
+            System.out.println("Stack Underflow");
+            return 0;
+        }
+        return root.data;
+
     } 
 
 	//Driver code