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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,66 @@ | ||
| const std = @import("std"); | ||
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| const Allocator = std.mem.Allocator; | ||
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| fn number_of_digits(n: u64) u8 { | ||
| return 1 + std.math.log10_int(n); | ||
| } | ||
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| fn split(n: u64) ?[2]u64 { | ||
| var exponent: u8 = 1; | ||
| var power_of_ten: u64 = 10; | ||
| var sep: u64 = 1; | ||
| while (power_of_ten <= n) { | ||
| exponent += 1; | ||
| power_of_ten *= 10; | ||
| if (exponent % 2 == 0) | ||
| sep *= 10; | ||
| } | ||
| if (exponent % 2 != 0) | ||
| return null; | ||
| return .{ @divTrunc(n, sep), n % sep }; | ||
| } | ||
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| fn _how_many(blinks: u7, stone: u64) u64 { | ||
| if (stone == 0) { | ||
| return switch (blinks) { | ||
| 1, 2 => 1, | ||
| else => how_many(blinks - 2, 2024), | ||
| }; | ||
| } | ||
| if (split(stone)) |pair| { | ||
| return if (blinks == 1) 2 else how_many(blinks - 1, pair[0]) + how_many(blinks - 1, pair[1]); | ||
| } | ||
| return if (blinks == 1) 1 else how_many(blinks - 1, stone * 2024); | ||
| } | ||
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| var cache: std.AutoHashMapUnmanaged(struct { u7, u64 }, u64) = .empty; | ||
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| fn how_many(blinks: u7, stone: u64) u64 { | ||
| if (cache.get(.{ blinks, stone })) |value| { | ||
| return value; | ||
| } | ||
| const value = _how_many(blinks, stone); | ||
| cache.putAssumeCapacity(.{ blinks, stone }, value); | ||
| return value; | ||
| } | ||
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| pub fn main() !void { | ||
| const input = [_]u64{ 2, 77706, 5847, 9258441, 0, 741, 883933, 12 }; | ||
| const blinks = 75; | ||
| var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator); | ||
| defer arena.deinit(); | ||
| const alloc = arena.allocator(); | ||
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| try cache.ensureTotalCapacity(alloc, 140_000); | ||
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| var result: u64 = 0; | ||
| var timer = try std.time.Timer.start(); | ||
| for (input) |stone| { | ||
| result += how_many(blinks, stone); | ||
| } | ||
| const time = timer.read(); | ||
| std.debug.print("Number of stones after {} blinks: {}\n", .{ blinks, result }); | ||
| std.debug.print("{}\n", .{std.fmt.fmtDuration(time)}); | ||
| std.debug.print("cache entries: {}\n", .{cache.count()}); | ||
| } |
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