AdventOfCode-2023/day01-hard/src/main.zig

const std = @import("std");

// Cannot believe I'm doing this by hand,
// but both somewhat popular regex libraries for Zig
// have build scripts incompatible with latest Zig 0.11 (released on August 4th, 2023),
// and I'm not into trying to link this with regex.h

fn get_digit_at_start(substr: []const u8) ?u8 {
    return switch (substr[0]) {
        '0'...'9' => substr[0] - '0',
        'o' => if (substr.len >= 3 and substr[1] == 'n' and substr[2] == 'e') 1 else null,
        't' => if (substr.len >= 3)
            switch (substr[1]) {
                'w' => if (substr[2] == 'o') 2 else null,
                'h' => if (substr.len >= 5 and substr[2] == 'r' and substr[3] == 'e' and substr[4] == 'e') 3 else null,
                else => null,
            }
        else
            null,
        'f' => if (substr.len >= 4)
            switch (substr[1]) {
                'o' => if (substr[2] == 'u' and substr[3] == 'r') 4 else null,
                'i' => if (substr[2] == 'v' and substr[3] == 'e') 5 else null,
                else => null,
            }
        else
            null,
        's' => if (substr.len >= 3)
            switch (substr[1]) {
                'i' => if (substr[2] == 'x') 6 else null,
                'e' => if (substr.len >= 5 and substr[2] == 'v' and substr[3] == 'e' and substr[4] == 'n') 7 else null,
                else => null,
            }
        else
            null,
        'e' => if (substr.len >= 5 and substr[1] == 'i' and substr[2] == 'g' and substr[3] == 'h' and substr[4] == 't') 8 else null,
        'n' => if (substr.len >= 4 and substr[1] == 'i' and substr[2] == 'n' and substr[3] == 'e') 9 else null,
        else => null,
    };
}

fn get_digit_at_end(substr: []const u8) ?u8 {
    const last = substr.len - 1;
    return switch (substr[last]) {
        '0'...'9' => substr[last] - '0',
        'e' => if (substr.len >= 3)
            switch (substr[last - 1]) {
                'n' => switch (substr[last - 2]) {
                    'o' => 1,
                    'i' => if (substr.len >= 4 and substr[last - 3] == 'n') 9 else null,
                    else => null,
                },
                'e' => if (substr.len >= 5 and substr[last - 2] == 'r' and substr[last - 3] == 'h' and substr[last - 4] == 't') 3 else null,
                'v' => if (substr.len >= 4 and substr[last - 2] == 'i' and substr[last - 3] == 'f') 5 else null,
                else => null,
            }
        else
            null,
        'o' => if (substr.len >= 3 and substr[last - 1] == 'w' and substr[last - 2] == 't') 2 else null,
        'r' => if (substr.len >= 4 and substr[last - 1] == 'u' and substr[last - 2] == 'o' and substr[last - 3] == 'f') 4 else null,
        'x' => if (substr.len >= 3 and substr[last - 1] == 'i' and substr[last - 2] == 's') 6 else null,
        'n' => if (substr.len >= 5 and substr[last - 1] == 'e' and substr[last - 2] == 'v' and substr[last - 3] == 'e' and substr[last - 4] == 's') 7 else null,
        't' => if (substr.len >= 5 and substr[last - 1] == 'h' and substr[last - 2] == 'g' and substr[last - 3] == 'i' and substr[last - 4] == 'e') 8 else null,
        else => null,
    };
}

fn get_first_digit(str: []const u8) u8 {
    for (0..str.len) |i| {
        const digit = get_digit_at_start(str[i..]);
        if (digit != null) {
            return digit.?;
        }
    }

    return 0;
}

fn get_last_digit(str: []const u8) u8 {
    for (0..str.len) |i| {
        const digit = get_digit_at_end(str[0 .. str.len - i]);
        if (digit != null) {
            return digit.?;
        }
    }

    return 0;
}

fn get_value(str: []const u8) u8 {
    const first_digit = get_first_digit(str);
    const last_digit = get_last_digit(str);
    return first_digit * 10 + last_digit;
}

pub fn main() !void {
    const stdout = std.io.getStdOut().writer();

    const raw_in = std.io.getStdIn();
    var buffered_reader = std.io.bufferedReader(raw_in.reader());
    var reader = buffered_reader.reader();

    var result: u32 = 0;
    var line_buffer: [1000]u8 = undefined;
    while (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')) |line| {
        result += get_value(line);
    }
    try stdout.print(
        "{d}\n",
        .{result},
    );
}

test "get digit at start" {
    try std.testing.expectEqual(@as(?u8, 1), get_digit_at_start("one"));
    try std.testing.expectEqual(@as(?u8, 1), get_digit_at_start("one!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("on"));

    try std.testing.expectEqual(@as(?u8, 2), get_digit_at_start("two"));
    try std.testing.expectEqual(@as(?u8, 2), get_digit_at_start("two!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("tw"));

    try std.testing.expectEqual(@as(?u8, 3), get_digit_at_start("three"));
    try std.testing.expectEqual(@as(?u8, 3), get_digit_at_start("three!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("thre"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("thre!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("thr!e"));

    try std.testing.expectEqual(@as(?u8, 4), get_digit_at_start("four"));
    try std.testing.expectEqual(@as(?u8, 4), get_digit_at_start("four!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("fou"));

    try std.testing.expectEqual(@as(?u8, 5), get_digit_at_start("five"));
    try std.testing.expectEqual(@as(?u8, 5), get_digit_at_start("five!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("fiv"));

    try std.testing.expectEqual(@as(?u8, 6), get_digit_at_start("six"));
    try std.testing.expectEqual(@as(?u8, 6), get_digit_at_start("six!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("si"));

    try std.testing.expectEqual(@as(?u8, 7), get_digit_at_start("seven"));
    try std.testing.expectEqual(@as(?u8, 7), get_digit_at_start("seven!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("seve"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("s!ven"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("sev!n"));

    try std.testing.expectEqual(@as(?u8, 8), get_digit_at_start("eight"));
    try std.testing.expectEqual(@as(?u8, 8), get_digit_at_start("eight!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("eigh"));

    try std.testing.expectEqual(@as(?u8, 9), get_digit_at_start("nine"));
    try std.testing.expectEqual(@as(?u8, 9), get_digit_at_start("nine!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("nin"));

    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("!!!!!!!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("t!!!!!!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("f!!!!!!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("s!!!!!!"));

    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("t"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("f"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_start("s"));
}

test "get digit at end" {
    try std.testing.expectEqual(@as(?u8, 1), get_digit_at_end("one"));
    try std.testing.expectEqual(@as(?u8, 1), get_digit_at_end("!one"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("ne"));

    try std.testing.expectEqual(@as(?u8, 2), get_digit_at_end("two"));
    try std.testing.expectEqual(@as(?u8, 2), get_digit_at_end("!two"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("wo"));

    try std.testing.expectEqual(@as(?u8, 3), get_digit_at_end("three"));
    try std.testing.expectEqual(@as(?u8, 3), get_digit_at_end("!three"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("hree"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("thre!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("thr!e"));

    try std.testing.expectEqual(@as(?u8, 4), get_digit_at_end("four"));
    try std.testing.expectEqual(@as(?u8, 4), get_digit_at_end("!four"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("our"));

    try std.testing.expectEqual(@as(?u8, 5), get_digit_at_end("five"));
    try std.testing.expectEqual(@as(?u8, 5), get_digit_at_end("!five"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("ive"));

    try std.testing.expectEqual(@as(?u8, 6), get_digit_at_end("six"));
    try std.testing.expectEqual(@as(?u8, 6), get_digit_at_end("!six"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("ix"));

    try std.testing.expectEqual(@as(?u8, 7), get_digit_at_end("seven"));
    try std.testing.expectEqual(@as(?u8, 7), get_digit_at_end("!seven"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("even"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("s!ven"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("sev!n"));

    try std.testing.expectEqual(@as(?u8, 8), get_digit_at_end("eight"));
    try std.testing.expectEqual(@as(?u8, 8), get_digit_at_end("!eight"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("ight"));

    try std.testing.expectEqual(@as(?u8, 9), get_digit_at_end("nine"));
    try std.testing.expectEqual(@as(?u8, 9), get_digit_at_end("!nine"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("ine"));

    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("!!!!!!!"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("!!!!!!e"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("!!!!!ne"));

    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("e"));
    try std.testing.expectEqual(@as(?u8, null), get_digit_at_end("ne"));
}

test "get first digit" {
    try std.testing.expectEqual(@as(?u8, 1), get_first_digit("1"));
    try std.testing.expectEqual(@as(?u8, 1), get_first_digit("!1"));
    try std.testing.expectEqual(@as(?u8, 1), get_first_digit("one"));
    try std.testing.expectEqual(@as(?u8, 1), get_first_digit("onetwo"));
    try std.testing.expectEqual(@as(?u8, 1), get_first_digit("oone"));
    try std.testing.expectEqual(@as(?u8, 1), get_first_digit("onone"));
    try std.testing.expectEqual(@as(?u8, 5), get_first_digit("fiveight"));
    try std.testing.expectEqual(@as(?u8, 8), get_first_digit("seveight"));
    try std.testing.expectEqual(@as(?u8, 0), get_first_digit("seveigh!"));
}

test "get last digit" {
    try std.testing.expectEqual(@as(?u8, 1), get_last_digit("1"));
    try std.testing.expectEqual(@as(?u8, 1), get_last_digit("1!"));
    try std.testing.expectEqual(@as(?u8, 1), get_last_digit("one"));
    try std.testing.expectEqual(@as(?u8, 1), get_last_digit("twoone"));
    try std.testing.expectEqual(@as(?u8, 1), get_last_digit("onee"));
    try std.testing.expectEqual(@as(?u8, 1), get_last_digit("onene"));
    try std.testing.expectEqual(@as(?u8, 8), get_last_digit("fiveight"));
    try std.testing.expectEqual(@as(?u8, 7), get_last_digit("sevene"));
    try std.testing.expectEqual(@as(?u8, 0), get_last_digit("!evene"));
}

test "get value" {
    // Oopsie! Thankfully the author of the puzzle didn't see this coming 🤪
    try std.testing.expectEqual(@as(?u8, 21), get_value("twone"));
    try std.testing.expectEqual(@as(?u8, 58), get_value("fiveight"));
}