Implement Queue using Stacks

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

class Queue {


public:
     stack<int>res;
    // Push element x to the back of queue.
    void push(int x) {
        stack<int>test;

        while(res.empty()!=true)
        {
            test.push(res.top());
            res.pop();
        }
        test.push(x);
        while(test.empty()!=true)
        {
             res.push(test.top());
             test.pop();
        }

    }

    // Removes the element from in front of queue.
    void pop(void) {
     res.pop();
    }

    // Get the front element.
    int peek(void) {
        return res.top();
    }

    // Return whether the queue is empty.
    bool empty(void) {
        return res.empty();
    }
};
posted @ 2015-11-28 20:03  djiankuo  阅读(127)  评论(0编辑  收藏  举报