advent-of-code-2023/day2/main.zig

const std = @import("std");

pub fn main() !void {
    const file = try std.fs.cwd().openFile("./data.txt", .{});
    defer file.close();

    var buffer: [30000]u8 = undefined;
    _ = try file.readAll(&buffer);

    var it = std.mem.split(u8, &buffer, "\n");

    var total1: u64 = 0;
    var total2: u64 = 0;

    while (it.next()) |line| {
        if (!std.ascii.isAlphanumeric(line[0])) {
            continue;
        }

        var game: u64 = 0;
        var busted: bool = false;

        var min_red: u64 = 1;
        var min_green: u64 = 1;
        var min_blue: u64 = 1;

        // Split the row on colons
        var parts = std.mem.split(u8, line, ": ");

        while (parts.next()) |part| {
            // if it contais "Game", parse out the game ID
            if (std.mem.eql(u8, part[0..4], "Game")) {
                game = try std.fmt.parseInt(u8, part[5..], 10);
            } else {
                // Split the turns up by semicolons
                var turns = std.mem.split(u8, part, "; ");

                var red: u64 = 0;
                var green: u64 = 0;
                var blue: u64 = 0;

                while (turns.next()) |turn| {
                    // Split the colors up by commas
                    var colors = std.mem.split(u8, turn, ", ");

                    while (colors.next()) |color| {
                        const idx = findIdx(color, ' ').?;
                        const num = try std.fmt.parseInt(u8, color[0..idx], 10);

                        if (endsWith(color, "red")) {
                            if (num > min_red) {
                                min_red = num;
                            }
                            if (num > 12) {
                                busted = true;
                            }
                            red += num;
                        } else if (endsWith(color, "green")) {
                            if (num > min_green) {
                                min_green = num;
                            }
                            if (num > 13) {
                                busted = true;
                            }
                            green += num;
                        } else if (endsWith(color, "blue")) {
                            if (num > min_blue) {
                                min_blue = num;
                            }
                            if (num > 14) {
                                busted = true;
                            }
                            blue += num;
                        }
                    }
                }
            }
        }

        if (!busted) {
            total1 += game;
        }

        const power: u64 = min_red * min_green * min_blue;
        total2 += power;
    }

    std.debug.print("part 1 total: {any}\n", .{total1});
    std.debug.print("part 2 total: {any}\n", .{total2});
}

// does the outer string end with the inner string
fn endsWith(outer: []const u8, inner: []const u8) bool {
    if (outer.len < inner.len) {
        return false;
    }

    const offset = outer.len - inner.len;

    for (inner, 0..) |c, idx| {
        if (c != outer[idx + offset]) {
            return false;
        }
    }

    return true;
}

// find the index of char in string
fn findIdx(string: []const u8, char: u8) ?usize {
    for (string, 0..) |c, idx| {
        if (c == char) {
            return idx;
        }
    }

    return null;
}