剑指 Offer 009. 用两个栈实现队列 栈

地址 https://leetcode-cn.com/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof/

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

解答

 

代码

class CQueue {
public:
    stack<int> stN;
    stack<int> stR;
    int curr ;
    CQueue() {
         while (!stN.empty()) {
            stN.pop();
        }
        while (!stR.empty()) {
            stR.pop();
        }
    }
    
    void appendTail(int value) {
        stN.push(value);
    }
    
    int deleteHead() {
        while(!stN.empty()){
            int val = stN.top();stN.pop();
            stR.push(val);
        }
        int ret = -1;
        if(!stR.empty()){
             ret = stR.top(); stR.pop();         
        }
        while(!stR.empty()){
            int val = stR.top(); stR.pop();
            stN.push(val);
        }
       
        return ret;
    }
};

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