/**

*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.

**/

class Queue {

public:

// Push element x to the back of queue.

void push(int x) {

a.push(x);

}

// Removes the element from in front of queue.

void pop(void) {

if(!b.empty())

b.pop();

else

{

while(!a.empty())

{

b.push(a.top());

a.pop();

}

b.pop();

}

}

// Get the front element.

int peek(void) {

if(!b.empty())

return b.top();

else

{

while(!a.empty())

{

b.push(a.top());

a.pop();

}

return b.top();

}

}

// Return whether the queue is empty.

bool empty(void) {

return (a.empty() && b.empty());

}

private:

stack<int> a,b;

};