contests/advent_of_code/2021/d8/main.cpp

#include <bits/stdc++.h>

using namespace std;

string file_name = "8.txt";
// string file_name = "test_text.txt";

vector<pair<array<string, 10>, array<string, 4>>> input_text;

pair<array<string, 10>, array<string, 4>> parse_line(const string &s){
    istringstream ss(s);
    pair<array<string, 10>, array<string, 4>> result;
    string word;

    for(size_t i = 0; i < 10; ++i){
        ss >> word;

        result.first[i] = word;
    }

    // There should be a pipe | here, which doesn't need to be put into the strings
    ss >> word;

    for(size_t i = 0; i < 4; ++i){
        ss >> word;

        result.second[i] = word;
    }

    return result;
}

map<string, int> identify_digits(const array<string, 10> &digits){
    map<int, string> digit_strings;

    vector<string> size_fives;
    vector<string> size_six;

    for(size_t i = 0; i < 10; ++i){
        size_t ds = digits[i].size();

        if(ds == 2){
            digit_strings[1] = digits[i];
        } else if(ds == 3){
            digit_strings[7] = digits[i];
        } else if(ds == 4){
            digit_strings[4] = digits[i];
        } else if(ds == 7){
            digit_strings[8] = digits[i];
        } else if(ds == 5){
            size_fives.push_back(digits[i]);
        } else if(ds == 6){
            size_six.push_back(digits[i]);
        }
    }

    vector<set<char>> size_fives_sets(3);
    for(int i = 0; i < 3; ++i){
        for(char &c : size_fives[i]){
            size_fives_sets[i].insert(c);
        }

        // We know that 2 is the only digit that combines with 4 to be 8
        for(char &c : digit_strings[4]){
            size_fives_sets[i].insert(c);
        }

        if(size_fives_sets[i].size() == 7){
            digit_strings[2] = size_fives[i];
            size_fives.erase(size_fives.begin() + i);
            break;
        }
    }

    // Now do kind of the same thing but for 5 and 3, combined with 7
    set<char> three_or_five;
    for(char &c : size_fives[0]){
        three_or_five.insert(c);
    }

    for(char &c : digit_strings[7]){
        three_or_five.insert(c);
    }

    // So in the case that it not of size 5, which means it is the number 5
    if(three_or_five.size() != 5){
        swap(size_fives[0], size_fives[1]);
    }

    digit_strings[3] = size_fives[0];
    digit_strings[5] = size_fives[1];

    vector<set<char>> size_six_sets(3);
    for(int i = 0; i < 3; ++i){
        for(char &c : size_six[i]){
            size_six_sets[i].insert(c);
        }

        // Only 6 and 7 together form 8 from all the six sized digits
        for(char &c : digit_strings[7]){
            size_six_sets[i].insert(c);
        }

        if(size_six_sets[i].size() == 7){
            digit_strings[6] = size_six[i];
            size_six.erase(size_six.begin() + i);
            break;
        }
    }

    // Now we only need 9 and 0, which can be distinguished by combining with 4
    set<char> nine_or_zero;
    for(char &c : size_six[0]){
        nine_or_zero.insert(c);
    }

    for(char &c : digit_strings[4]){
        nine_or_zero.insert(c);
    }

    // In the case that the size is 7, which means it combines to an eight
    if(nine_or_zero.size() != 7){
        swap(size_six[0], size_six[1]);
    }

    digit_strings[0] = size_six[0];
    digit_strings[9] = size_six[1];

    for(auto &s : digit_strings){
        sort(s.second.begin(), s.second.end());
    }

    map<string, int> result;
    for(auto &d : digit_strings){
        result[d.second] = d.first;
    }

    return result;
}

int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);


    ifstream file_stream;
    file_stream.open(file_name);

    if(file_stream.is_open()){
        string line;

        while(getline(file_stream, line)){
            input_text.push_back(parse_line(line));
        }

        file_stream.close();
    }


    // Testing the input parsing

    // cout << input_text.size() << endl;
    // for(const auto &line : input_text){
    //     for(auto word : line.first){
    //         cout << word << " ";
    //     }

    //     cout << "| ";

    //     for(auto word : line.second){
    //         cout << word << " ";
    //     }

    //     cout << endl;
    // }

    int result = 0;
    for(const auto &line : input_text){
        for(size_t i = 0; i < 4; ++i){
            size_t w = line.second[i].size();
            if(w == 2 || w == 4 || w == 3 || w == 7){
                result++;
            }
        }
    }

    cout << result << endl;

    result = 0;
    for(auto &line : input_text){
        auto digit_map = identify_digits(line.first);

        int acc = 0;
        for(int i = 0; i < 4; ++i){
            string s = line.second[i];
            sort(s.begin(), s.end());

            acc *= 10;
            acc += digit_map[s];
        }

        result += acc;
    }

    cout << result << endl;

    cout << flush;

    return 0;
}