_ = @import("day15.zig");

    const day15 = @import("day15.zig");

const days = 14;

const days = 15;

const std = @import("std");
const INPUT = "14,3,1,0,9,5";
const Str = []const u8;
pub fn first(allocator: ?std.mem.Allocator) anyerror!usize {
    return try getLast(allocator.?, INPUT, 2020);
}
pub fn second(allocator: ?std.mem.Allocator) anyerror!usize {
    return try getLast(allocator.?, INPUT, 30_000_000);
}
fn getLast(allocator: std.mem.Allocator, input: Str, limit: usize) !usize {
    var spoken = std.AutoHashMap(usize, usize).init(allocator);
    defer spoken.deinit();
    var starting = std.mem.tokenize(u8, input, ",");
    var last: usize = undefined;
    var round: usize = 1;
    while (starting.next()) |st| : (round += 1) {
        const num = try std.fmt.parseUnsigned(usize, st, 0);
        try spoken.put(num, round);
        last = num;
    }
    // Van Eck Sequence
    round -= 1;
    while (round < limit) : (round += 1) {
        const next = round - (spoken.get(last) orelse round);
        try spoken.put(last, round);
        last = next;
    }
    return last;
}
test "day15a" {
    try std.testing.expectEqual(@as(usize, 614), try first(std.testing.allocator));
}
test "day15b" {
    try std.testing.expectEqual(@as(usize, 1065), try second(std.testing.allocator));
}