aoc-2020-zig

main.zig (3635B)

const std = @import("std");
const aoc = @import("aoc");

const BagCount = struct { id: u64, count: u32 };

const BagRule = struct {
    outer: u64,
    innerit: std.mem.SplitIterator(u8),

    fn from(line: []const u8) BagRule {
        var partit = std.mem.split(u8, line, " bags contain ");
        const outer = std.hash.CityHash64.hash(partit.next().?);
        var innerit = std.mem.split(u8, partit.next().?, ", ");
        return BagRule{ .outer = outer, .innerit = innerit };
    }

    fn nextInner(self: *BagRule) !?BagCount {
        if (self.innerit.next()) |bagstr| {
            if (std.mem.eql(u8, bagstr[0..2], "no")) return null;
            const lastsep = std.mem.lastIndexOfScalar(u8, bagstr, ' ').?;
            const firstsep = std.mem.indexOfScalar(u8, bagstr, ' ').?;
            const count = try std.fmt.parseInt(u32, bagstr[0..firstsep], 10);
            const id = std.hash.CityHash64.hash(bagstr[firstsep + 1 .. lastsep]);
            return BagCount{ .id = id, .count = count };
        } else {
            return null;
        }
    }
};

fn countBagsTotal(map: *std.AutoHashMap(u64, std.ArrayList(BagCount)), outer: u64) u64 {
    var sum: u64 = 0;
    if (map.get(outer)) |inner| {
        for (inner.items) |bag|
            sum += bag.count * (1 + countBagsTotal(map, bag.id));
    }
    return sum;
}

fn countParentTypes(map: *std.AutoHashMap(u64, std.ArrayList(u64)), inner: u64, seen: *std.ArrayList(u64)) anyerror!u64 {
    var sum: u64 = 0;
    if (map.get(inner)) |outer| {
        for (outer.items) |bagid| {
            if (std.mem.indexOfScalar(u64, seen.items, bagid) == null) {
                try seen.append(bagid);
                sum += 1 + try countParentTypes(map, bagid, seen);
            }
        }
    }
    return sum;
}

fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
    _ = args;

    var lineit = std.mem.tokenize(u8, input, "\n");
    var map = std.AutoHashMap(u64, std.ArrayList(u64)).init(allocator);
    defer {
        var mapit = map.iterator();
        while (mapit.next()) |kv| kv.value_ptr.deinit();
        map.deinit();
    }

    while (lineit.next()) |line| {
        var rule = BagRule.from(line);
        while (try rule.nextInner()) |inner| {
            if (map.get(inner.id) == null)
                try map.put(inner.id, std.ArrayList(u64).init(allocator));
            try map.getEntry(inner.id).?.value_ptr.append(rule.outer);
        }
    }

    const target = std.hash.CityHash64.hash("shiny gold");
    var seen = std.ArrayList(u64).init(allocator);
    defer seen.deinit();

    const answer = try countParentTypes(&map, target, &seen);

    return try std.fmt.allocPrint(allocator, "{d}", .{answer});
}

fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
    _ = args;

    var lineit = std.mem.tokenize(u8, input, "\n");
    var map = std.AutoHashMap(u64, std.ArrayList(BagCount)).init(allocator);
    defer {
        var mapit = map.iterator();
        while (mapit.next()) |kv| kv.value_ptr.deinit();
        map.deinit();
    }

    const target = std.hash.CityHash64.hash("shiny gold");
    while (lineit.next()) |line| {
        var rule = BagRule.from(line);
        if (map.get(rule.outer) == null)
            try map.put(rule.outer, std.ArrayList(BagCount).init(allocator));
        while (try rule.nextInner()) |bag| {
            try map.getEntry(rule.outer).?.value_ptr.append(bag);
        }
    }

    const answer = countBagsTotal(&map, target);

    return try std.fmt.allocPrint(allocator, "{d}", .{answer});
}

pub const main = aoc.main(part1, part2, .{ "161", "30899" });