面试题09

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

Solutions

• The same as problem 232.

• straight forward

class CQueue {
public:
    stack<int> input, output;
    CQueue() {

    }

    void appendTail(int value) {
        input.push(value);
    }

    int deleteHead() {
        if (!output.size()) {
            while (input.size()) {
                output.push(input.top());
                input.pop();
            }
            if (!output.size())
                return -1;
        }
        int front = output.top();
        output.pop();
        return front;
    }
};

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