AdventOfCode-2023/day07-easy/src/main.zig

const std = @import("std");

fn StackList(comptime T: type, comptime capacity_type: type, comptime capacity: capacity_type) type {
    return struct {
        const Self = @This();
        mem: [capacity]T,
        length: capacity_type,

        fn add(self: *Self, value: T) void {
            self.mem[self.length] = value;
            self.length += 1;
        }

        fn has(self: *Self, needle: T) bool {
            for (0..self.length) |i| {
                if (self.mem[i] == needle) {
                    return true;
                }
            }

            return false;
        }

        fn getMutableSlice(self: *Self) []T {
            return (&self.mem)[0..self.length];
        }

        fn getSlice(self: *const Self) []const T {
            return self.mem[0..self.length];
        }

        fn init() Self {
            return Self{
                .mem = undefined,
                .length = 0,
            };
        }
    };
}

const Rank = enum(u8) {
    Five = 6,
    Four = 5,
    FullHouse = 4,
    Three = 3,
    TwoPair = 2,
    OnePair = 1,
    HighCard = 0,
};

const Hand = packed struct(u64) {
    bid: u16,
    card5: u8,
    card4: u8,
    card3: u8,
    card2: u8,
    card1: u8,
    rank: Rank,
};

const HandSet = StackList(Hand, usize, 1000);

fn parseCard(char: u8) u8 {
    return switch (char) {
        '2'...'9' => char - '0',
        'T' => 10,
        'J' => 11,
        'Q' => 12,
        'K' => 13,
        'A' => 14,
        else => unreachable,
    };
}

fn getRank(cards: [5]u8) Rank {
    var quantities = std.mem.zeroes([6]u8);
    for (cards) |first_card| {
        var matches: u4 = 0;
        for (cards) |second_card| {
            if (first_card == second_card) {
                matches += 1;
            }
        }

        quantities[matches] += 1;
    }

    if (quantities[5] != 0) {
        return .Five;
    }

    if (quantities[4] != 0) {
        return .Four;
    }

    if (quantities[3] != 0) {
        if (quantities[2] != 0) {
            return .FullHouse;
        } else {
            return .Three;
        }
    }

    if (quantities[2] == 4) {
        return .TwoPair;
    }

    if (quantities[2] != 0) {
        return .OnePair;
    }

    return .HighCard;
}

fn addDigit(result: anytype, digit: u8) void {
    result.* = (result.* * 10) + (digit - '0');
}

fn parseHand(line: []u8) Hand {
    var cards: [5]u8 = undefined;
    var i: usize = 0;
    while (i < 5) : (i += 1) {
        cards[i] = parseCard(line[i]);
    }

    var bid: u16 = 0;
    i = 6;
    while (i < line.len) : (i += 1) {
        addDigit(&bid, line[i]);
    }

    return .{
        .rank = getRank(cards),
        .card1 = cards[0],
        .card2 = cards[1],
        .card3 = cards[2],
        .card4 = cards[3],
        .card5 = cards[4],
        .bid = bid,
    };
}

fn cmpByValue(context: void, a: Hand, b: Hand) bool {
    return std.sort.asc(u64)(context, @bitCast(a), @bitCast(b));
}

fn solve(hands: *HandSet) u64 {
    std.sort.heap(Hand, hands.getMutableSlice(), {}, cmpByValue);
    var result: u64 = 0;
    for (hands.getSlice(), 1..) |hand, i| {
        result += i * hand.bid;
    }
    return result;
}

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 hands = HandSet.init();
    var line_buffer: [1000]u8 = undefined;
    while (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')) |line| {
        hands.add(parseHand(line));
    }
    try stdout.print("{d}\n", .{solve(&hands)});
}