225. Implement Stack using Queues（Stack-Easy）

转载请注明作者和出处：http://blog.csdn.net/c406495762

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).

题目： 使用队列实现栈。只能使用一些简单的队列操作，例如push(x)、pop()、top()、empty()。我是使用一个队列实现一个栈。

Language:cpp

class MyStack {
public:
    /** Initialize your data structure here. */
    MyStack() {
    }

    queue<int> que;      

    /** 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 i = que.front();
        que.pop();
        return i;
    }

    /** Get the top element. */
    int top() {
        return que.front();
    }

    /** Returns whether the stack is empty. */
    bool empty() {
        return que.empty();
    }
};

/** * 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(); */