LeetCode 面试题09. 用两个栈实现队列

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

 

class CQueue {
private:
    stack input, output;

public:
    CQueue() {

    }
    
    void appendTail(int value) {
        input.push(value);
    }
    
    int deleteHead() {
        if (!output.empty())
        {
            int val = output.top();
            output.pop();
            return val;
        }
        else if (!input.empty())
        {
            while (!input.empty())
            {
                output.push(input.top());
                input.pop();
            }
            int val = output.top();
            output.pop();
            return val;
        }
        else
            return -1;
    }
};

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