main.zig (1761B)
1const std = @import("std"); 2const aoc = @import("aoc"); 3 4fn transform(subject_num: u64, loops: u64) u64 { 5 var num: u64 = 1; 6 var i: u64 = 0; 7 while (i < loops) : (i += 1) { 8 num *= subject_num; 9 num %= 20201227; 10 } 11 return num; 12} 13 14fn bfLoops(subject_num: u64, pubkey: u64) ?u64 { 15 var i: u64 = 0; 16 var tmp: u64 = 1; 17 while (i < ~@as(u64, 0)) : (i += 1) { 18 if (tmp == pubkey) return i; 19 tmp *= subject_num; 20 tmp %= 20201227; 21 } 22 return null; 23} 24 25fn parseInput(door_pubkey: *u64, card_pubkey: *u64, input: []const u8) !void { 26 var lineit = std.mem.tokenize(u8, input, "\n"); 27 door_pubkey.* = try std.fmt.parseInt(u64, try aoc.unwrap(lineit.next()), 10); 28 card_pubkey.* = try std.fmt.parseInt(u64, try aoc.unwrap(lineit.next()), 10); 29} 30 31fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 { 32 var door_pubkey: u64 = undefined; 33 var card_pubkey: u64 = undefined; 34 35 try parseInput(&door_pubkey, &card_pubkey, input); 36 37 if (args.len == 0 or std.mem.eql(u8, args[0], "bf_door")) { 38 if (bfLoops(7, door_pubkey)) |door_loops| { 39 std.debug.print("{}\n", .{transform(card_pubkey, door_loops)}); 40 return null; 41 } 42 } else if (args.len > 0 and std.mem.eql(u8, args[0], "bf_card")) { 43 if (bfLoops(7, card_pubkey)) |card_loops| { 44 const answer = transform(door_pubkey, card_loops); 45 return try std.fmt.allocPrint(allocator, "{}", .{answer}); 46 } 47 } 48 return null; 49} 50 51fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 { 52 _ = input; 53 _ = args; 54 55 return try std.fmt.allocPrint(allocator, "", .{}); 56} 57 58pub const main = aoc.main(part1, part2, .{ "15217943", "" });