implement-stack-using-queues(AC).cpp

// 1AC, This problem is silly.
// Why make things difficult to prove you're smart?
// You're supposed to make things easier with your brilliance.
#include <queue>
using namespace std;

class Stack {
public:
	Stack() {
		f = 0;
		nf = !f;
	}
	
    // Push element x onto stack.
    void push(int x) {
		q[nf].push(x);
    }

    // Removes the element on top of the stack.
    void pop() {
		while (q[nf].size() > 1) {
			q[f].push(q[nf].front());
			q[nf].pop();
		}
		if (q[nf].size() == 1) {
			q[nf].pop();
			return;
		}
		
		while (q[f].size() > 1) {
			q[nf].push(q[f].front());
			q[f].pop();
		}
		f = nf;
		nf = !f;
		
		q[nf].pop();
    }

    // Get the top element.
    int top() {
		while (q[nf].size() > 1) {
			q[f].push(q[nf].front());
			q[nf].pop();
		}
		if (q[nf].size() == 1) {
			return q[nf].front();
		}
		
		while (q[f].size() > 1) {
			q[nf].push(q[f].front());
			q[f].pop();
		}
		f = nf;
		nf = !f;
		
		return q[nf].front();
    }

    // Return whether the stack is empty.
    bool empty() {
		return q[f].size() + q[nf].size() == 0;
    }
private:
	queue<int> q[2];
	int f, nf;
};