#Leetcode# 225. Implement Stack using Queues

https://leetcode.com/problems/implement-stack-using-queues/

 

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.

Example:

MyStack stack = new MyStack();

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

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).

代码：

class MyStack {
public:
    /** Initialize your data structure here. */
    MyStack() {}
    
    /** Push element x onto stack. */
    void push(int x) {
        s.push(x);
    }
    
    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        int t = s.top();
        s.pop();
        return t;
    }
    
    /** Get the top element. */
    int top() {
        if(!s.empty()) return s.top();
        return 0;
    }
    
    /** Returns whether the stack is empty. */
    bool empty() {
        if(s.size() == 0) return true;
        return false;
    }
    private:
        stack<int> s;
};

/**
 * 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();
 */

　　难道只能靠这样的题续命了么。。。被搞得头大死了