Date and Time [Mockvita 2]

    // Author - Aman Vishwakarma
    // Laptop 2 [Arch VM 2]

    #include<iostream>
    #include<vector>
    #include<utility>
    #include<queue>
    #include<stack>
    #include<math.h>
    #include<algorithm>
    #include<string>
    using namespace std;
    #define whatis(x) cout<<#x<<" : "<<x<<endl
    int days[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    int hashfn[10] = {} ;
    int months(int i) {
        int temp = i;
            int l  = temp % 10;
            temp = temp / 10;
            if( ( l != temp ) && hashfn[l]>0 && hashfn[temp] > 0)  {
                hashfn[l]--;
                hashfn[temp]--;
                return i;
            }
            else if( l == temp && hashfn[l]>1 ) {
                    hashfn[l]--;
                    hashfn[l]--;
                    return i;
            }
    return -1;
    }
    vector<int> switch2pre (vector<int> &upd) {
        vector<int> upd2(10, 0);
        for(int i = 0; i<10; i++) {
            hashfn[i] = upd[i];
            upd2[i] = upd[i];
        }
        return upd2;
    }
    vector<int> updated () {
        vector<int> upd2(10, 0);
        for(int i = 0; i<10; i++) {

            upd2[i] = hashfn[i];
        }
        return upd2;
    }
    int main() {
        vector<int> upd(10, 0);
        for(int i = 0; i<12; i++) {
            int d;
            char ch;
            cin>>d;
            if(i != 11)
            cin>>ch;
            hashfn[d]++;
            upd[d]++;
        }
        //initialised
        int mm = -1, dd = -1, hh = -1, ss = -1;
        for(int i = 12; i>0; i--) {
            //For MONTHS
            vector<int> upd2 = switch2pre(upd);

            mm = months(i);
            if(mm != -1) {
                upd2 = updated();

                for(int j = days[i-1]; j>0; j--) {
                //For DAYS
                    vector<int> upd3 = switch2pre(upd2);

                    dd = months(j);

                    if(dd!=-1) {
                        upd3 = updated();

                        for(int k =23; k>=0; k--) {
                            //For HOURS
                            vector<int> upd4 = switch2pre(upd3);

                            hh = months(k);

                            if(hh != -1) {
                                upd4 = updated();

                                for(int z = 59; z>=0; z-- ){
                                    //FOR SECONDS
                                    vector<int> upd5 = switch2pre(upd4);

                                    ss = months(z);

                                    if(ss != -1) break;
                                }
                            if(ss!=-1)
                            break;
                            }
                            }
                    if(ss!=-1)
                    break;
                    }
                }
            if(ss!=-1)
            break;
            }
        }
        if( mm == -1 || ss == -1 || dd == -1 | hh == -1) cout<<0;
        else printf("%02d/%02d %02d:%02d", mm, dd, hh, ss);


        return 0;
    }