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).
Update (2015-06-11):

The class name of the Java function had been updated to
MyStack instead of Stack.

分析:
      只有push,需要一次移动，其他都一样

代码：

class Stack {
public:
queue<int> q;
// Push element x onto stack.
void push(int x) {
q.push(x);
for(int i=1; i<q.size(); i++)
{
q.push(q.front());
q.pop();
}
}

// Removes the element on top of the stack.
void pop() {
q.pop();
}

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

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