【剑指Offer系列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 )

代码

Python

class CQueue:

    def __init__(self):
        # A存储, B辅助
        self.A, self.B = [], []

    def appendTail(self, value: int) -> None:
        self.A.append(value)
    
    def deleteHead(self) -> int:
        # B非空
        if self.B: return self.B.pop()
        # A为空
        if not self.A: return -1
        # A非空
        while self.A:
            self.B.append(self.A.pop())
        return self.B.pop()

# Your CQueue object will be instantiated and called as such:
# obj = CQueue()
# obj.appendTail(value)
# param_2 = obj.deleteHead()

C++

class CQueue {
public:
    // A存储, B辅助
    stack<int> A;
    stack<int> B;
    
    CQueue() {}
    
    void appendTail(int value) {
        A.push(value);
    }
    
    int deleteHead() {
        // A为空
        if (A.empty()) return -1;
        
        // A非空
        while (!A.empty()) {
            int tmp1=A.top();
            A.pop();
            B.push(tmp1);
        }
        int res=B.top();
        B.pop();
        // B非空
        while (!B.empty()) {
            int tmp2=B.top();
            B.pop();
            A.push(tmp2);
        }
        return res;
    }
};

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