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).

class Stack {

public:

// Push element x onto stack.

void push(int x) {

Q.push(x);

}

// Removes the element on top of the stack.

void pop() {

int n = Q.size();

for(int i = 0;i<n-1;i++)

{

Q.push(Q.front());

Q.pop();

}

Q.pop();

}

// Get the top element.

int top() {

int n = Q.size();

for(int i = 0;i<n-1;i++)

{

Q.push(Q.front());

Q.pop();

}

int front = Q.front();

Q.pop();Q.push(front);

return front;

}

// Return whether the stack is empty.

bool empty() {

return Q.empty();

}

private:

queue<int> Q;

};