aoc 2020 day 7

parts_1_and_2.cpp

#include <QDebug>
#include <QFile>
#include <QHash>
#include <QTextStream>

struct InnerBag
{
    QString name;
    int count;
};

void holders(const QMultiHash<QString, QString> &hash, QSet<QString> &results, QString bagName)
{
    auto vals = hash.values(bagName);
    for (const auto &val : vals)
    {
        results.insert(val);
        holders(hash, results, val);
    }
}

void expense(const QMultiHash<QString, InnerBag> &hash, int &result, QString bagName, int mul)
{
    auto vals = hash.values(bagName);
    for (const auto &val : vals)
    {
        result += val.count * mul;
        expense(hash, result, val.name, mul * val.count);
    }
}

int main(int, char **)
{
    QMultiHash<QString, QString> outers;
    QMultiHash<QString, InnerBag> inners;
    QSet<QString> holdsMyBag;
    QFile f("input.txt");
    f.open(QIODevice::ReadOnly);
    QTextStream ts(&f);
    QString line;
    while (!ts.atEnd())
    {
        ts.readLineInto(&line);
        int b1 = line.indexOf("bags");
        QString outer = line.left(b1).trimmed();
        line = line.right(line.size() - (b1 + 13));
        QStringList parts = line.split(',');
        if (parts.size() == 1 && parts.at(0) == "no other bags.") continue;
        for (auto &part : parts)
        {
            QString x = part.trimmed();
            int n = x.left(x.indexOf(' ')).toInt();
            x = x.right(x.size() - x.indexOf(' ') - 1).remove(" bags").remove(" bag").remove('.');
            outers.insert(x, outer);
            InnerBag ib;
            ib.name = x;
            ib.count = n;
            inners.insert(outer, ib);
        }
    }
    f.close();
    QString myBag = "shiny gold";
    holders(outers, holdsMyBag, myBag);
    int totalcost = 0;
    expense(inners, totalcost, myBag, 1);
    qInfo() << holdsMyBag.count();
    qInfo() << totalcost;
}

35 minutes to create this solution. Didn't want to fuss with fiddly string stuff this time, so I just used a wasteful sledgehammer. Spent about 5 minutes cleaning it up before posting. Here's the non-cleaned-up version: https://gist.github.com/randrew/df1b4a31fb14692c0117edc6fdfb74ca