[leetcode] 232. 用栈实现队列

LeetCode.232 用栈实现队列

public class MyQueue {

    Stack<Integer> push;
    Stack<Integer> pop;

    /**
     * Initialize your data structure here.
     */
    public MyQueue() {
        push = new Stack<Integer>();
        pop = new Stack<Integer>();
    }

    /**
     * Push element x to the back of queue.
     */
    public void push(int x) {
        push.push(x);
    }

    /**
     * Removes the element from in front of queue and returns that element.
     */
    public int pop() {
        if (pop.isEmpty()) {
            while (!push.isEmpty()) {
                pop.push(push.pop());
            }
        }

        return pop.pop();
    }

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

        return pop.peek();
    }

    /**
     * Returns whether the queue is empty.
     */
    public boolean empty() {
        return pop.isEmpty() && push.isEmpty();
    }
}