From 2e4a2962b19647b8b03bf3f55e86555d74d50d8a Mon Sep 17 00:00:00 2001
From: Antoine <angagnie@student.42.fr>
Date: Wed, 11 Dec 2024 07:43:57 +0100
Subject: [PATCH] 2024 day 11

---
 2024/11/solve.zig | 66 +++++++++++++++++++++++++++++++++++++++++++++++
 README.md         |  6 ++---
 2 files changed, 69 insertions(+), 3 deletions(-)
 create mode 100644 2024/11/solve.zig

diff --git a/2024/11/solve.zig b/2024/11/solve.zig
new file mode 100644
index 0000000..53c1e05
--- /dev/null
+++ b/2024/11/solve.zig
@@ -0,0 +1,66 @@
+const std = @import("std");
+
+const Allocator = std.mem.Allocator;
+
+fn number_of_digits(n: u64) u8 {
+    return 1 + std.math.log10_int(n);
+}
+
+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 };
+}
+
+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);
+}
+
+var cache: std.AutoHashMapUnmanaged(struct { u7, u64 }, u64) = .empty;
+
+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;
+}
+
+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();
+
+    try cache.ensureTotalCapacity(alloc, 140_000);
+
+    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()});
+}
diff --git a/README.md b/README.md
index 55a757a..388ab1f 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,7 @@ My solutions for the [Advent of Code](https://adventofcode.com), a challenge sta
 | 08  |||||:star::star:|:star::star:|:star::star:|:star::star:|:star::star:
 | 09  |||||:star::star:|:star::star:|:star::star:|:star::star:|:star::star:
 | 10  |||||:star::star:|:star::star:|:star::star:|:star::star:|
-| 11  |||||:star::star:|:star::star:|:star::star:|:star::star:|
+| 11  |||||:star::star:|:star::star:|:star::star:|:star::star:|:star::star:
 | 12  |||||:star::star:|:star::star:|:star::star:|:star::star:|
 | 13  |||||:star::star:|:star::star:|:star::star:|:star::star:|:star::star:
 | 14  |||||:star::star:|:star::star:|:star::star:|:star::star:|
@@ -30,6 +30,6 @@ My solutions for the [Advent of Code](https://adventofcode.com), a challenge sta
 | 23  |||||||:star::star:|:star:|
 | 24  ||||||:star::star:|:star::star:|:star:|
 | 25  |||||:star:|:star:|:star::star:||
-| Total | 10 | 14 | 4 | 10 | 42 | 44 | 50 | 44 | 20
+| Total | 10 | 14 | 4 | 10 | 42 | 44 | 50 | 44 | 22
 
-Total stars: 238
+Total stars: 240