Implement Queue using Stacks

Implement the following operations of a queue using stacks.

• 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.

 

class MyQueue {
	public Stack<Integer> stackPush;
	public Stack<Integer> stackPop;
	
	public MyQueue() {
		stackPush = new Stack<Integer>();
		stackPop = new Stack<Integer>();
	}
    // Push element x to the back of queue.
    public void push(int x) {
    	stackPush.push(x);
    }

    // Removes the element from in front of queue.
    public void pop() {
        if (stackPop.isEmpty() && stackPush.isEmpty()) {
        	;
        } else if (stackPop.isEmpty()) {
        	while (!stackPush.isEmpty()) {
        		stackPop.push(stackPush.pop());
        	}
        }
        stackPop.pop();
    }

    // Get the front element.
    public int peek() {
    	if (stackPop.isEmpty() && stackPush.isEmpty()) {
        	return 0;
    	} else if (stackPop.isEmpty()) {
        	while (!stackPush.isEmpty()) {
        		stackPop.push(stackPush.pop());
        	}
        }
    	return stackPop.peek();
    }

    // Return whether the queue is empty.
    public boolean empty() {
        return stackPop.isEmpty() && stackPush.isEmpty();
    }
}