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package stack;

import java.util.Stack;

/**

* Created by gouthamvidyapradhan on 29/07/2017. Implement the following operations of a queue using

* stacks.

*

* <p>push(x) -- Push element x to the back of queue. pop() -- Removes the element from in front of

* queue. peek() -- Get the front element. empty() -- Return whether the queue is empty.

*

* <p>Notes: You must use only standard operations of a stack -- which means only push to top,

* peek/pop from top, size, and is empty operations are valid. Depending on your language, stack may

* not be supported natively. You may simulate a stack by using a list or deque (double-ended

* queue), as long as you use only standard operations of a stack. You may assume that all

* operations are valid (for example, no pop or peek operations will be called on an empty queue).

*/

public class MyQueue {

private Stack<Integer> stack;

public static void main(String[] args) throws Exception {

MyQueue myQueue = new MyQueue();

myQueue.push(5);

myQueue.push(12);

myQueue.push(7);

myQueue.push(9);

System.out.println(myQueue.peek());

System.out.println(myQueue.pop());

myQueue.push(56);

myQueue.push(53);

System.out.println(myQueue.pop());

}

/** Initialize your data structure here. */

public MyQueue() {

stack = new Stack<>();

}

/** Push element x to the back of queue. */

public void push(int x) {

stack.push(x);

}

/** Removes the element from in front of queue and returns that element. */

public int pop() {

Stack<Integer> auxStack = new Stack<>();

while (!stack.isEmpty()) {

auxStack.push(stack.pop());

}

int result = auxStack.pop();

while (!auxStack.isEmpty()) {

stack.push(auxStack.pop());

}

return result;

}

/** Get the front element. */

public int peek() {

Stack<Integer> auxStack = new Stack<>();

while (!stack.isEmpty()) {

auxStack.push(stack.pop());

}

int result = auxStack.peek();

while (!auxStack.isEmpty()) {

stack.push(auxStack.pop());

}

return result;

}

/** Returns whether the queue is empty. */

public boolean empty() {

return stack.isEmpty();

}

}