advent-of-code-2023/day4/main.zig

const std = @import("std");

const Card = struct { winning: std.ArrayList(u8), have: std.ArrayList(u8), copies: u64 };

pub fn main() !void {
    const content = @embedFile("data.txt");
    var cards = try parseCards(content);
    defer cards.deinit();

    var score1 = try findScore(&cards, 1);
    std.debug.print("part 1: {d}\n", .{score1});

    _ = try findScore(&cards, 2);
    var numCards: u128 = 0;
    for (cards.items) |c| {
        numCards += c.copies;
    }

    std.debug.print("part 2: {any}\n", .{numCards});
}

fn findScore(cards: *std.ArrayList(Card), part: u8) !u64 {
    var total: u64 = 0;
    // iterate over all cards
    for (cards.items, 0..) |card, i| {
        var numWinners: usize = 0;
        var score: u32 = 0;
        // iterate over the numbers we have
        for (card.have.items) |n| {
            // and the winning numbers
            for (card.winning.items) |w| {
                if (n == w) {
                    numWinners += 1;
                    score = if (score == 0) 1 else score * 2;
                }
            }
        }

        if (part == 2) {
            for (0..numWinners) |j| {
                cards.items[i + j + 1].copies += card.copies;
            }
        }

        total += score;
    }

    return total;
}

fn parseCards(content: []const u8) !std.ArrayList(Card) {
    var lines = std.mem.split(u8, content, "\n");

    var cards = std.ArrayList(Card).init(std.heap.page_allocator);

    while (lines.next()) |line| {
        if (line.len == 0) {
            continue;
        }

        // break line up on :
        var parts = std.mem.split(u8, line, ": ");
        _ = parts.next();
        // break the 2nd part up by |
        var sections = std.mem.split(u8, parts.next().?, " | ");
        // split the left part up on spaces
        var nums = std.mem.split(u8, sections.next().?, " ");

        var winning = std.ArrayList(u8).init(std.heap.page_allocator);
        while (nums.next()) |d| {
            if (d.len > 0) {
                try winning.append(try std.fmt.parseInt(u8, d, 10));
            }
        }

        // split the right part up on spaces
        nums = std.mem.split(u8, sections.next().?, " ");

        var have = std.ArrayList(u8).init(std.heap.page_allocator);
        while (nums.next()) |d| {
            if (d.len > 0) {
                try have.append(try std.fmt.parseInt(u8, d, 10));
            }
        }

        try cards.append(Card{ .winning = winning, .have = have, .copies = 1 });
    }

    return cards;
}