From 16d6e05deba693047cf979de0e0be891f51b2b73 Mon Sep 17 00:00:00 2001
From: jmug <u.g.a.mariano@gmail.com>
Date: Thu, 12 Dec 2024 00:49:04 -0800
Subject: [PATCH] Solved day 11, had to look at reddit for this one to catch
 up!

Signed-off-by: jmug <u.g.a.mariano@gmail.com>
---
 src/day11.zig | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 src/day11.zig

diff --git a/src/day11.zig b/src/day11.zig
new file mode 100644
index 0000000..18bc622
--- /dev/null
+++ b/src/day11.zig
@@ -0,0 +1,60 @@
+const std = @import("std");
+const print = std.debug.print;
+
+const ResType = enum {
+    Single,
+    Pair,
+};
+
+const Res = union(ResType) {
+    Single: u128,
+    Pair: std.meta.Tuple(&.{ u128, u128 }),
+};
+
+fn blink(stone: u128) Res {
+    if (stone == 0) {
+        return Res{ .Single = 1 };
+    }
+    // return (a * std.math.pow(u64, 10, std.math.log10(b) + 1)) + b;
+    const digits = std.math.log10(stone) + 1;
+    if (digits % 2 == 0) {
+        const left = stone / std.math.pow(u128, 10, digits / 2);
+        const right = stone - (left * std.math.pow(u128, 10, digits / 2));
+        return Res{ .Pair = .{ left, right } };
+    }
+    return Res{ .Single = stone * 2024 };
+}
+
+fn stonesAfterBlinks(stone: u128, blinks: u8, cache: *[76]std.AutoHashMap(u128, u128)) !u128 {
+    if (blinks == 0) {
+        return 1;
+    }
+    if (cache[blinks].get(stone)) |s| {
+        return s;
+    }
+    const res = switch (blink(stone)) {
+        ResType.Single => |s| try stonesAfterBlinks(s, blinks - 1, cache),
+        ResType.Pair => |p| try stonesAfterBlinks(p[0], blinks - 1, cache) + try stonesAfterBlinks(p[1], blinks - 1, cache),
+    };
+    try cache[blinks].put(stone, res);
+    return res;
+}
+
+pub fn main() !void {
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const allocator = arena.allocator();
+
+    const stones: [8]u128 = .{ 64554, 35, 906, 6, 6960985, 5755, 975820, 0 };
+    // const stones: [2]u128 = .{ 125, 17 };
+    var cache: [76]std.AutoHashMap(u128, u128) = undefined;
+    for (0..76) |i| {
+        cache[i] = std.AutoHashMap(u128, u128).init(allocator);
+    }
+
+    var total: u128 = 0;
+    for (0..stones.len) |si| {
+        total += try stonesAfterBlinks(stones[si], 75, &cache);
+    }
+    print("Stones after 75 blinks: {d}\n", .{total});
+}