Leetcode刷题101-225. 用队列实现栈(C++详细解法！！！)

Come from : [https://leetcode-cn.com/problems/implement-stack-using-queues/submissions/]

1.Question

Implement the following operations of a stack using queues.

push(x) – Push element x onto stack.
pop() – Removes the element on top of the stack.
top() – Get the top element.
empty() – Return whether the stack is empty.

Notes:

1. You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
2. Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
3. You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

Example :

MyStack stack = new MyStack();

stack.push(1);
stack.push(2);  
stack.top();   // returns 2
stack.pop();   // returns 2
stack.empty(); // returns false

2.Answer

easy 类型题目。.不多BB


AC代码如下：

class MyStack {
public:
    /** Initialize your data structure here. */
    MyStack() {
        
    }
    
    /** Push element x onto stack. */
    void push(int x) {
        queue<int> temp_queue;   //定义一个临时队列，利用该队列进行原始data_queue元素 与新元素的 次序交换
        temp_queue.push(x);
        while(!data.empty())
        {
            temp_queue.push(data.front());
            data.pop();
        }
        while(!temp_queue.empty())
        {
            data.push(temp_queue.front());
            temp_queue.pop();
        }
    }
    
    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        int temp = data.front();      //取栈顶元素，相当于取 队列头部元素
        data.pop();                   //弹出队列头部元素
        return temp;                  //返回栈顶的元素，相当于返回队列的头部元素
    }
    
    /** Get the top element. */
    int top() {
        return data.front();        //获取栈顶元素，等于 返回队列头部元素
    }
    
    /** Returns whether the stack is empty. */
    bool empty() {
        return data.empty();
    }
    
private:
    queue<int> data;                //data数据队列存储元素的顺序，就是栈存储元素的顺序
};

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

3.我的收获

栈，队列。。。
fighting。。。

2019/6/16 胡云层 于南京 101