[C++知识库]力扣-232题 用栈实现队列（C++）

题目链接：https://leetcode-cn.com/problems/implement-queue-using-stacks/
题目如下：

class MyQueue {
public:
    stack<int> stk1;
    stack<int> stk2;
    /** Initialize your data structure here. */
    MyQueue() {
        
    }
    
    /** Push element x to the back of queue. */
    void push(int x) {
        //将元素压入堆栈stk1
        stk1.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        //将元素放到stk2，拿到最先放入stk1的元素，并移除，再放回stk1
        int num;
        while(!stk1.empty()){
            num=stk1.top();
            stk1.pop();
            stk2.push(num);
        }
        num=stk2.top();
        stk2.pop();

        int num1;
        while(!stk2.empty()){
            num1=stk2.top();
            stk2.pop();
            stk1.push(num1);
        }

        return num;

    }
    
    /** Get the front element. */
    int peek() {
        //将元素依次放到stk2，拿到最后一个出栈的元素，再还原回去
        int num;
        while(!stk1.empty()){
            num=stk1.top();
            stk1.pop();
            stk2.push(num);
        }

        int num1;
        while(!stk2.empty()){
            num1=stk2.top();
            stk2.pop();
            stk1.push(num1);
        }

        return num;

    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        return stk1.empty()&&stk2.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();
 */