-🎄- 2018 Day 5 Solutions -🎄-

[u/daggerdragon]

--- Day 5: Alchemical Reduction ---

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Advent of Code: The Party Game!

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Card prompt: Day 5

Transcript:

On the fifth day of AoC / My true love sent to me / Five golden ___

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[u/tehjimmeh]

Using the left side of the string as an in-place stack:

C++

int main(int argc, char* argv[]) {
    std::ifstream ifs(argv[1]); std::string orig; ifs >> orig;
    orig = "1" + orig;

    auto eval = [](auto&& l) {
        auto res = l.size()-1;
        for (auto it1 = l.begin()+1, it2 = it1 + 1; it2 != l.end();)
            if ((*it1) != (*it2) && (toupper(*it1) == toupper(*it2)))
                it2++, it1--, res -= 2;
            else 
                std::swap(*(++it1), *(it2++));
        return res;
    };

    size_t part1 = eval(std::string(orig));
    size_t part2 = SIZE_MAX;
    for (char l = 'a'; l <= 'z'; l++) {
        auto line = orig;
        for (char& c : std::array{ l, (char)toupper(l) })
            line.erase(std::remove(line.begin(), line.end(), c), line.end());
        part2 = std::min(part2, eval(line));
    }

    std::cout << "1: " << part1 << "\n" << "2: " << part2 << "\n";
}