From 1c704680a887b5a78ec82671db0d78f06526defb Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Wed, 11 Dec 2024 09:05:52 +0200
Subject: [PATCH] aoc2024: Implement day11 solution

Finally we got a problem where trivial solution does not work
---
 userspace/aoc2024/CMakeLists.txt       |   1 +
 userspace/aoc2024/day11/CMakeLists.txt |   9 ++
 userspace/aoc2024/day11/main.cpp       | 120 +++++++++++++++++++++++++
 3 files changed, 130 insertions(+)
 create mode 100644 userspace/aoc2024/day11/CMakeLists.txt
 create mode 100644 userspace/aoc2024/day11/main.cpp

diff --git a/userspace/aoc2024/CMakeLists.txt b/userspace/aoc2024/CMakeLists.txt
index 5e608ad2..ebb7312d 100644
--- a/userspace/aoc2024/CMakeLists.txt
+++ b/userspace/aoc2024/CMakeLists.txt
@@ -9,6 +9,7 @@ set(AOC2024_PROJECTS
 	day8
 	day9
 	day10
+	day11
 	full
 )
 
diff --git a/userspace/aoc2024/day11/CMakeLists.txt b/userspace/aoc2024/day11/CMakeLists.txt
new file mode 100644
index 00000000..f8d29c03
--- /dev/null
+++ b/userspace/aoc2024/day11/CMakeLists.txt
@@ -0,0 +1,9 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2024_day11 ${SOURCES})
+banan_include_headers(aoc2024_day11 ban)
+banan_link_library(aoc2024_day11 libc)
+
+install(TARGETS aoc2024_day11 OPTIONAL)
diff --git a/userspace/aoc2024/day11/main.cpp b/userspace/aoc2024/day11/main.cpp
new file mode 100644
index 00000000..da54b461
--- /dev/null
+++ b/userspace/aoc2024/day11/main.cpp
@@ -0,0 +1,120 @@
+#include <BAN/HashMap.h>
+#include <BAN/StringView.h>
+#include <BAN/Vector.h>
+
+#include <inttypes.h>
+#include <stdio.h>
+
+using i8  = int8_t;
+using i16 = int16_t;
+using i32 = int32_t;
+using i64 = int64_t;
+
+using u8  = uint8_t;
+using u16 = uint16_t;
+using u32 = uint32_t;
+using u64 = uint64_t;
+
+u64 even_divisor(u64 stone)
+{
+	u8 digits = 0;
+	for (u64 mult = 1; mult <= stone; mult *= 10)
+		digits++;
+
+	if (digits % 2)
+		return 0;
+
+	u64 divisor = 1;
+	for (u8 i = 0; i < digits / 2; i++)
+		divisor *= 10;
+
+	return divisor;
+}
+
+u64 count_stones(u64 stone, u8 depth)
+{
+	static BAN::HashMap<u64, u64> cache;
+
+	if (depth == 0)
+		return 1;
+
+	const u64 cache_key = (stone << 8) | depth;
+
+	auto it = cache.find(cache_key);
+	if (it != cache.end())
+		return it->value;
+
+	if (stone == 0)
+		return count_stones(1, depth - 1);
+
+	u64 divisor = even_divisor(stone);
+	if (divisor == 0)
+		return count_stones(stone * 2024, depth - 1);
+
+	u64 result = 0;
+	result += count_stones(stone / divisor, depth - 1);
+	result += count_stones(stone % divisor, depth - 1);
+	MUST(cache.insert(cache_key, result));
+	return result;
+}
+
+i64 part1(FILE* fp)
+{
+	BAN::Vector<u64> stones;
+
+	char buffer[128];
+	ASSERT (fgets(buffer, sizeof(buffer), fp));
+	{
+		auto strs = MUST(BAN::StringView(buffer).split(' '));
+		for (auto str : strs)
+			MUST(stones.push_back(atoll(str.data())));
+	}
+
+	u64 result = 0;
+	for (size_t i = 0; i < stones.size(); i++)
+		result += count_stones(stones[i], 25);
+
+	return result;
+}
+
+i64 part2(FILE* fp)
+{
+	BAN::Vector<u64> stones;
+
+	char buffer[128];
+	ASSERT (fgets(buffer, sizeof(buffer), fp));
+	{
+		auto strs = MUST(BAN::StringView(buffer).split(' '));
+		for (auto str : strs)
+			MUST(stones.push_back(atoll(str.data())));
+	}
+
+	u64 result = 0;
+	for (size_t i = 0; i < stones.size(); i++)
+		result += count_stones(stones[i], 75);
+
+	return result;
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2024/day11_input.txt";
+
+	if (argc >= 2)
+		file_path = argv[1];
+
+	FILE* fp = fopen(file_path, "r");
+	if (fp == nullptr)
+	{
+		perror("fopen");
+		return 1;
+	}
+
+	printf("part1: %" PRId64 "\n", part1(fp));
+
+	fseek(fp, 0, SEEK_SET);
+
+	printf("part2: %" PRId64 "\n", part2(fp));
+
+	fclose(fp);
+}