Skip to main content

9.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：

["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

代码​

class CQueue {
public:
    stack<int> tail, head;
    CQueue() {
         while (!tail.empty()) {
            tail.pop();
        }
        while (!head.empty()) {
            head.pop();
        }
    }
    
    void appendTail(int value) {
        this->tail.push(value);
    }
    
    int deleteHead() {
        if (head.empty()) {
            while (!tail.empty()) {
                head.push(tail.top());
                tail.pop();
            }
            
        }
        if (head.empty())   return -1;
        else {
            int res = head.top();
            head.pop();
            return res;
        }
        
    }
};

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