Java 代码

class MyQueue {

    Stack s1;
    Stack s2;

    /** Initialize your data structure here. */
    public MyQueue() {
        s1 = new Stack();
        s2 = new Stack();
    }

    /** Push element x to the back of queue. */
    public void push(int x) {
        s1.push(x);

    }

    /** Removes the element from in front of queue and returns that element. */
    public int pop() {

        while (!s1.empty())
            s2.push(s1.pop());

        int b = (int)s2.pop();

        while (!s2.empty())
            s1.push(s2.pop());

        return b;
    }

    /** Get the front element. */
    public int peek() {
        while (!s1.empty())
            s2.push(s1.pop());

        int b = (int)s2.peek();

        while (!s2.empty())
            s1.push(s2.pop());

        return b;

    }

    /** Returns whether the queue is empty. */
    public boolean empty() {

        return s1.empty();
    }
}