(leetcode)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.

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).

 

Update (2015-06-11):
The class name of the Java function had been updated to MyStack instead of Stack.

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and all test cases.

 

用一个队列就可实现，看了很多例子觉得discuss里面有个朋友写的很简练，就用了他的丝路，和她基本一致

class Stack {
public:
    // Push element x onto stack..
    queue<int> a;
    void push(int x) {
        a.push(x);
    }

    // Removes the element on top of the stack.
    void pop() {
        size_t i = 0;
        size_t size = a.size();
        for(i = 0; i < size-1; ++i)
        {
            a.push(a.front());
            a.pop();
        }
        a.pop();
    }

    // Get the top element.
    int top() {
        return a.back();
    }

    // Return whether the stack is empty.
    bool empty() {
        return a.empty();
    }
};