baekjoon/10845.cpp at main · simsgood2/baekjoon · GitHub

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#include <bits/stdc++.h>
#define FastIO                        \
    ios_base::sync_with_stdio(false); \
    cin.tie(NULL);                    \
    cout.tie(NULL);
using namespace std;

int main(void){
    FastIO;
    int n;
    cin>>n;
    queue<int> q;
    for(int i=0; i<n; i++){
        string str;
        cin>>str;
        if (str == "push") {
            int n;
            cin>>n;
            q.push(n);
        }
         else if (str == "pop") {
            if(q.empty()){
                cout<<-1<<'\n';
            }
            else{
                cout<<q.front()<<'\n';
                q.pop();
            }
        }
        else if(str =="size"){
            cout<<q.size()<<'\n';
        }
         else if(str == "empty"){
            if(q.empty()){
                cout<<1<<'\n';
            }
            else{
                cout<<0<<'\n';
            }
        }
        else if(str == "front"){
            if(q.empty()){
                cout<<-1<<'\n';
            }
            else{
                cout<<q.front()<<'\n';
            }
        }
        else if(str =="back"){
            if(q.empty()){
                cout<<-1<<'\n';
            }
            else{
                cout<<q.back()<<'\n';
            }
        }
    }
}