백준 10866번 덱 C++

#include <iostream>
#include <deque>
using namespace std;
//https://www.acmicpc.net/problem/10866

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	int n = 0;
	cin >> n;

	deque<int> d;
	string str = "";
	int num = 0;
	for (int i = 0; i < n; ++i) {
		cin >> str;
		if (str == "push_front") {
			cin >> num;
			d.push_front(num);
		}
		else if (str == "push_back") {
			cin >> num;
			d.push_back(num);
		}
		else if (str == "pop_front") {
			if (!d.empty()) {
				cout << d.front() << '\n';
				d.pop_front();
			}
			else cout << "-1\n";
		}
		else if (str == "pop_back") {
			if (!d.empty()) {
				cout << d.back() << '\n';
				d.pop_back();
			}
			else cout << "-1\n";
		}
		else if (str == "size")
			cout << d.size() << '\n';
		else if (str == "empty")
			if (d.empty()) cout << "1\n";
			else cout << "0\n";
		else if(str == "front")
			if (!d.empty())
				cout << d.front() << '\n';
			else cout << "-1\n";
		else if(str == "back")
			if (!d.empty())
				cout << d.back() << '\n';
			else cout << "-1\n";
	}
	
	return 0;
}

https://www.acmicpc.net/problem/10866

10866번: 덱