力扣——用栈实现队列

class MyQueue {

    private Stack<Integer> stackPush;
    private Stack<Integer> stackPop;

    /** Initialize your data structure here. */
    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 and returns that element. */
    public int pop() {
        if(stackPop.empty()){
            while(!stackPush.empty()){
                stackPop.push(stackPush.pop());
            }
        }
        return stackPop.pop();
    }

    /** Get the front element. */
    public int peek() {
        if(stackPop.empty()){
            while(!stackPush.empty()){
                stackPop.push(stackPush.pop());
            }
        }
        return stackPop.peek();
    }

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


/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue obj = new MyQueue();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.peek();
 * boolean param_4 = obj.empty();
 */