剑指9：用两个栈实现队列

传送门

nowcoder
leetcode

题目描述

两个栈实现一个队列，完成队列的 Push 和 Pop 操作。
队列中的元素为 int 类型。

C++ 代码 - nowcoder

class Solution
{
public:
    void push(int node) {
        pushStack.push(node);
    }

    int pop() {
        if (popStack.empty()) {
            while (!pushStack.empty()) {
                popStack.push(pushStack.top());
                pushStack.pop();
            }
        }

        if (popStack.empty()) {
            return -1;
        } else {
            int deleteItem = popStack.top();
            popStack.pop();
            return deleteItem;
        }
    }

private:
    stack<int> pushStack;
    stack<int> popStack;
};

C++ 代码 - leetcode

class CQueue {
public:
    CQueue() {

    }
    
    void appendTail(int value) {
        pushStack.push(value);
    }
    
    int deleteHead() {
        if (popStack.empty()) {
            while (!pushStack.empty()) {
                int t = pushStack.top();
                pushStack.pop();
                popStack.push(t);
            }
        }

        if (popStack.empty()) {
            return -1;
        }
        int t = popStack.top();
        popStack.pop();
        return t;
    }

private:
    stack<int> pushStack, popStack;
};