Leetcode刷题103-232. 用栈实现队列(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 queue using stacks.

push(x) – Push element x to the back of queue.
pop() – Removes the element from in front of queue.
peek() – Get the front element.
empty() – Return whether the queue is empty.

Notes:

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

Example :

MyQueue queue = new MyQueue();

queue.push(1);
queue.push(2);  
queue.peek();  // returns 1
queue.pop();   // returns 1
queue.empty(); // returns false

2.Answer

easy 类型题目。.不多BB（和前天的 101.用队列实现栈类似）。

AC代码如下：

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

/**
 * 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();
 */

3.我的收获

栈，队列。。。
fighting。。。

2019/6/18 胡云层 于南京 103