leetcode225.Implement Stack using Queues

题目

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:

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.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.You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

解法

题目的意思是用queue实现stack，直接在每次加入元素之后，将元素移动到队列的最开始即可。

注意：

只能使用题目中规定的几个函数

代码

class MyStack {public:    /** Initialize your data structure here. */    MyStack() {    }    /** Push element x onto stack. */    void push(int x) {        que.push(x);        for(int i = 0; i < que.size()-1; i ++)        {            que.push(que.front());            que.pop();        }    }    /** Removes the element on top of the stack and returns that element. */    int pop() {        int temp = que.front();        que.pop();        return temp;    }    /** Get the top element. */    int top() {        return que.front();    }    /** Returns whether the stack is empty. */    bool empty() {        return que.empty();    }private:    queue<int> que;};/** * 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(); */