LeetCode *** 225. 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：

利用queue扩展stack，用一个queue，然后用一个int数组来记录queue的值就可以了。

代码：

class Stack {
queue<int> myQ;

public:
// Push element x onto stack.
void push(int x) {
int size=myQ.size();
int *tmp=new int[size];

for(int i=0;i<size;++i){
tmp[i]=myQ.front();
myQ.pop();
}

myQ.push(x);

for(int i=0;i<size;++i)
myQ.push(tmp[i]);
}

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

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

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