CTCI Challange, DAY 6

Day 6:-

Program Statement:- A Tale of Two Stacks


On Paper:-

public static class MyQueue<T> {
        Stack<T> stackNewestOnTop = new Stack<>();
        Stack<T> stackOldestOnTop = new Stack<>();

        public void enqueue(T value) { // Push onto newest stack
            stackNewestOnTop.push(value);
        }

        public void dequeueOrPeek(int operation) {
            if (stackOldestOnTop.isEmpty()) {
                while (!stackNewestOnTop.isEmpty()) {
                    stackOldestOnTop.push(stackNewestOnTop.pop());
                }
            }
            if (operation == 2)
                stackOldestOnTop.pop();
            else
                System.out.println(stackOldestOnTop.peek());
        }
    }

    public static void main(String[] args) {
        MyQueue<Integer> queue = new MyQueue<>();

        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();

        for (int i = 0; i < n; i++) {
            int operation = scan.nextInt();
            if (operation == 1) { // enqueue
                queue.enqueue(scan.nextInt());
            } else if (operation == 2 || operation == 3) { // dequeue
                queue.dequeueOrPeek(operation);
            }
        }
        scan.close();
    }