Exercise_1.java

class Stack {
    //Please read sample.java file before starting.
    //Kindly include Time and Space complexity at top of each file
    static final int MAX = 1000;
    int top;
    int a[] = new int[MAX]; // Maximum size of Stack

    boolean isEmpty()
    {
        // Time Complexity : O(1)
        // Space Complexity : O(1)

        //Write your code here
        if(a.length == 0 || a == null){
            return true;
        }else{
            return false;
        }
    }

    Stack()
    {
        //Initialize your constructor
        top = -1;
    }


    boolean push(int x)
    {
        // Time Complexity : O(1)
        // Space Complexity : O(1)

        //Check for stack Overflow
        if(top < MAX - 1){
            top += 1;
            a[top]= x;
            return true;
        }else{
            System.out.println("***** Stack Overflow *****");
            return false;
        }
        //Write your code here
    }

    int pop()
    {
        // Time Complexity : O(1)
        // Space Complexity : O(1)

        //If empty return 0 and print " Stack Underflow"
        if(top < 0){
            System.out.print("***** Stack Underflow : ");
            return 0;
        }else{
            top -= 1;
            return a[top+1];
        }
        //Write your code here
    }

    int peek()
    {
        // Time Complexity : O(1)
        // Space Complexity : O(1)

        //Write your code here
        if(top == -1){
            return 0;
        }else{
            return a[top];
        }
    }
}

// Driver code
class Main {
    public static void main(String args[])
    {
        Stack s = new Stack();
        s.push(10);
        s.push(20);
        s.push(30);
        System.out.println(s.pop() + " Popped from stack");
        System.out.println(s.pop() + " Popped from stack");
        System.out.println(s.pop() + " Popped from stack");
        System.out.println(s.pop() + " Popped from stack");
    }
}