【剑指Offer】面试题09. 用两个栈实现队列

题目

用两个栈实现一个队列。队列的声明如下,请实现它的两个函数 appendTail 和 deleteHead ,分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素,deleteHead 操作返回 -1 )

示例 1:

输入:
["CQueue","appendTail","deleteHead","deleteHead"]
[[],[3],[],[]]
输出:[null,null,3,-1]

示例 2:

输入:
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[5],[2],[],[]]
输出:[null,-1,null,null,5,2]

提示:

  • 1 <= values <= 10000
  • 最多会对 appendTail、deleteHead 进行 10000 次调用

思路

代码

class CQueue {
    stack<int> st1;
    stack<int> st2;
public:
    CQueue() {
        
    }
    
    void appendTail(int value) {
        st1.push(value);
    }
    
    int deleteHead() {
        int res = -1;
        if (st1.empty() && st2.empty()) {
            return res;
        }
        if (st2.empty()) {
            while (!st1.empty()) {
                st2.push(st1.top());
                st1.pop();
            }
        }
        res = st2.top();
        st2.pop();  
        return res;
    }
};
posted @ 2020-02-16 21:30  Galaxy_hao  阅读(376)  评论(0编辑  收藏  举报