Player 1:
18
50
9
4
25
37
39
40
29
6
41
28
3
11
31
8
1
38
33
30
42
15
26
36
43
Player 2:
32
44
19
47
12
48
14
2
13
10
35
45
34
7
5
17
46
21
24
49
16
22
20
27
23

const std = @import("std");
const PATH = "input/day22.txt";
const Str = []const u8;
pub fn first(allocator: ?std.mem.Allocator) anyerror!usize {
    var game = try parseInput(allocator.?, @embedFile(PATH));
    defer {
        game.p1.deinit();
        game.p2.deinit();
    }
    try game.play();
    var sum: usize = 0;
    for (game.p1.items) |item, idx| {
        sum += (game.p1.items.len - idx) * item;
    }
    for (game.p2.items) |item, idx| {
        sum += (game.p2.items.len - idx) * item;
    }
    return sum;
}
pub fn second(allocator: ?std.mem.Allocator) anyerror!usize {
    _ = allocator;
    return 0;
}
const CardType = u6;
const Game = struct {
    round: usize = 0,
    p1: std.ArrayList(CardType),
    p2: std.ArrayList(CardType),
    fn play(self: *@This()) anyerror!void {
        if (self.p1.items.len == 0 or self.p2.items.len == 0) {
            return;
        }
        self.round += 1;
        const p1 = self.p1.orderedRemove(0);
        const p2 = self.p2.orderedRemove(0);
        if (p1 > p2) {
            try self.p1.append(p1);
            try self.p1.append(p2);
        } else {
            try self.p2.append(p2);
            try self.p2.append(p1);
        }
        try self.play();
    }
};
fn parseInput(allocator: std.mem.Allocator, input: Str) !Game {
    var ret = Game{
        .p1 = std.ArrayList(CardType).init(allocator),
        .p2 = std.ArrayList(CardType).init(allocator),
    };
    var lines = std.mem.split(u8, input, "\n");
    // Player 1
    while (lines.next()) |line| {
        if (line.len == 0) break;
        if (line[0] == 'P') continue;
        const num = try std.fmt.parseUnsigned(CardType, line, 10);
        try ret.p1.append(num);
    }
    // Player 2
    while (lines.next()) |line| {
        if (line.len == 0) break;
        if (line[0] == 'P') continue;
        const num = try std.fmt.parseUnsigned(CardType, line, 10);
        try ret.p2.append(num);
    }
    return ret;
}
test "day21a" {
    try std.testing.expectEqual(@as(usize, 33561), try first(std.testing.allocator));
}
test "day21b" {
    try std.testing.expectEqual(@as(usize, 0), try second(std.testing.allocator));
}
const test_input =
    \\Player 1:
    \\9
    \\2
    \\6
    \\3
    \\1
    \\
    \\Player 2:
    \\5
    \\8
    \\4
    \\7
    \\10
;