用栈实现队列

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

import java.util.Stack;

class CQueue {

    private Stack<Integer> s1;

    private Stack<Integer> s2;

    public CQueue() {
        this.s1 = new Stack<>();
        this.s2 = new Stack<>();
    }

    public void appendTail(int value) {
        s1.push(value);
    }

    public int deleteHead() {

        if (s2.isEmpty()) {
            while (! s1.isEmpty()) {
                s2.push(s1.pop());
            }

            if (s2.isEmpty()) {
                return -1;
            }
        }
        return s2.pop();
    }
}

/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue obj = new CQueue();
 * obj.appendTail(value);
 * int param_2 = obj.deleteHead();
 */

用栈实现队列

原文：https://blog.51cto.com/tianyiya/2530932