2021年3月5日每日一题
原题:232. 用栈实现队列

这道题就是字面意思，用栈来模拟队列
栈：先入后出
队列:先入先出

维护两个栈，一个负责接收，一个负责输出
这道题其实可以用vector来模拟也是一样的
c++代码如下：

class MyQueue {
public:
    /** Initialize your data structure here. */
    stack<int>a,b;
    MyQueue() {
        
        
    }
    
    /** Push element x to the back of queue. */
    void push(int x) {
        a.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        int ans = this->peek();
        b.pop();
        return ans;
    }
    
    /** Get the front element. */
    int peek() {
        if(b.empty()){
            while(!a.empty()){
                b.push(a.top());
                a.pop();
            }
        }
        return b.top();
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        return a.empty() && b.empty();
    }
};

/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue* obj = new MyQueue();
 * obj->push(x);
 * int param_2 = obj->pop();
 * int param_3 = obj->peek();
 * bool param_4 = obj->empty();
 */

结果