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Source code

const std = @import("std");

fn Character(
    comptime character_count: comptime_int,
) type {
    return std.math.IntFittingRange(
        0,
        character_count + 1, // +1 for whitespace
    );
}

fn maxIndex(
    comptime word_length: comptime_int,
    comptime character_count: comptime_int,
) comptime_int {
    const a: comptime_int = std.math.powi(usize, character_count + 1, word_length) catch unreachable;
    return a - 1;
}

fn Index(
    comptime word_length: comptime_int,
    comptime character_count: comptime_int,
) type {
    return std.math.IntFittingRange(0, maxIndex(word_length, character_count));
}

fn hash(
    comptime word_length: comptime_int,
    comptime character_count: comptime_int,
    word: [word_length]Character(character_count),
) Index(word_length, character_count) {
    const adjusted_character_count = character_count + 1; // 1 for whitespace
    var count: [adjusted_character_count]std.math.IntFittingRange(0, character_count) = .{0} ** adjusted_character_count;
    for (word) |char| count[char] += 1;
    const Result = Index(word_length, character_count);
    var result: Result = 0;
    var base: Result = 1;
    for (count[1..], 1..) |this_char_count, character| {
        const first_term = character * base;
        const pow = std.math.powi(Result, adjusted_character_count, this_char_count) catch unreachable;
        base *= pow;
        const multiplier = @divExact(pow - 1, character_count);
        const to_add = first_term * multiplier;
        result += @intCast(to_add);
    }
    return result;
}

pub fn main() void {
    const testHash = test_namespace.testHash;
    testHash("");
    testHash("A");
    testHash("AABC");
    testHash("BCAA");
    testHash("ZZZZZZZ");
}