백준 10845 큐

문제 링크 : **https://www.acmicpc.net/problem/10845**
※ 선행해야 할 알고리즘 : 큐

//kuklife.tistory.com
#include<iostream>
#include<queue>
#include<string>
using namespace std;
int check(queue<int> q)
{
	if (q.empty()) return -1;
	else return 0;
}
int main()
{
	int n;
	queue<int> q;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		string str;
		cin >> str;

		if (str == "push")
		{
			int in;
			cin >> in;
			q.push(in);
		}
		else if (str == "front")
		{
			if (check(q) == -1) cout << -1 << endl;
			else cout << q.front() << endl;
		}
		else if (str == "back")
		{
			if (check(q) == -1) cout << -1 << endl;
			else cout << q.back() << endl;
		}
		else if (str == "size")
			cout << q.size() << endl;
		else if (str == "empty")
			cout << q.empty() << endl;
		else if (str == "pop")
		{
			if (check(q) == -1) cout << -1 << endl;
			else
			{
				cout << q.front() << endl;
				q.pop();
			}
		}

	}
}