백준 18258 : 큐 2

https://www.acmicpc.net/problem/18258

18258번: 큐 2

 

#include <iostream>
#include <deque>
#include <string>
using namespace std;

int n, a;
string s;
deque<int> q;
int main() {
	ios::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	cin >> n;
	while (n--) {
		cin >> s;
		if (s == "push") {
			cin >> a;
			q.push_back(a);
		}
		else if (s == "front") {
			cout << (q.empty() ? -1 : q.front()) << "\n";
		}
		else if (s == "back") {
			cout << (q.empty() ? -1 : q.back()) << "\n";
		}
		else if (s == "pop") {
			if (q.empty()) {
				cout << "-1\n";
			}
			else {
				cout << q.front() << "\n";
				q.pop_front();
			}
		}
		else if (s == "empty") {
			cout << (q.empty() ? 1 : 0) << "\n";
		}
		else {
			cout << q.size() << "\n";
		}
	}
}