[백준 10866] 덱

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

int main(){
    deque<int>dq;
    int n;
    cin >> n;

    for(int i=0; i<n; i++){
        string cmd; cin >> cmd;

        if(cmd == "push_front"){
            int x; cin >> x;
            dq.push_front(x);
        }
        else if(cmd == "push_back"){
            int x; cin >> x;
            dq.push_back(x);
        }
        else if(cmd == "pop_front"){
            if(dq.empty()) cout << -1 << '\n';
            else{
                cout << dq.front() << '\n';
                dq.pop_front();
            }
        }
        else if(cmd == "pop_back") {
            if(dq.empty()) cout << -1 << '\n';
            else {
                cout << dq.back() << '\n';
                dq.pop_back();
            }
        }
        else if(cmd == "size") {
            cout << (int)dq.size() << '\n';
        }
        else if(cmd == "empty") {
            cout << dq.empty() << '\n';
        }
        else if(cmd == "front") {
            if(dq.empty()) cout << -1 << '\n';
            else cout << dq.front() << '\n';
        }
        else if(cmd == "back") {
            if(dq.empty()) cout << -1 << '\n';
            else cout << dq.back() << '\n';
        }
    }

    return 0;
   
}