From 8b612ba547e2eeb99768c89e2975297cff7900c2 Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Mon, 9 Dec 2024 16:20:21 +0200
Subject: [PATCH] aoc2024: Implement day9 solution

part2 is kinda unoptimized, it should not use expanded input, but I did
not feel like rewriting my parsing code :)
---
 userspace/aoc2024/CMakeLists.txt      |   1 +
 userspace/aoc2024/day9/CMakeLists.txt |   9 ++
 userspace/aoc2024/day9/main.cpp       | 153 ++++++++++++++++++++++++++
 3 files changed, 163 insertions(+)
 create mode 100644 userspace/aoc2024/day9/CMakeLists.txt
 create mode 100644 userspace/aoc2024/day9/main.cpp

diff --git a/userspace/aoc2024/CMakeLists.txt b/userspace/aoc2024/CMakeLists.txt
index 8f5bf874..c01b6cbe 100644
--- a/userspace/aoc2024/CMakeLists.txt
+++ b/userspace/aoc2024/CMakeLists.txt
@@ -7,6 +7,7 @@ set(AOC2024_PROJECTS
 	day6
 	day7
 	day8
+	day9
 	full
 )
 
diff --git a/userspace/aoc2024/day9/CMakeLists.txt b/userspace/aoc2024/day9/CMakeLists.txt
new file mode 100644
index 00000000..df13d03b
--- /dev/null
+++ b/userspace/aoc2024/day9/CMakeLists.txt
@@ -0,0 +1,9 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2024_day9 ${SOURCES})
+banan_include_headers(aoc2024_day9 ban)
+banan_link_library(aoc2024_day9 libc)
+
+install(TARGETS aoc2024_day9 OPTIONAL)
diff --git a/userspace/aoc2024/day9/main.cpp b/userspace/aoc2024/day9/main.cpp
new file mode 100644
index 00000000..85d35dbb
--- /dev/null
+++ b/userspace/aoc2024/day9/main.cpp
@@ -0,0 +1,153 @@
+#include <BAN/Vector.h>
+
+#include <ctype.h>
+#include <inttypes.h>
+#include <stdio.h>
+
+using i8  = int8_t;
+using i16 = int16_t;
+using i32 = int32_t;
+using i64 = int64_t;
+using isize = ssize_t;
+
+using u8  = uint8_t;
+using u16 = uint16_t;
+using u32 = uint32_t;
+using u64 = uint64_t;
+using usize = size_t;
+
+static BAN::Vector<u32> parse_input(FILE* fp)
+{
+	BAN::Vector<u32> result;
+
+	u32 idx = 0;
+
+	char buffer[1024];
+	while (fgets(buffer, sizeof(buffer), fp))
+	{
+		usize len = strlen(buffer);
+		if (len > 0 && buffer[len - 1] == '\n')
+			len--;
+
+		for (usize i = 0; i < len; i++)
+		{
+			const u32 block_id = (idx % 2) ? 0xFFFFFFFF : idx / 2;
+
+			ASSERT(isdigit(buffer[i]));
+			for (i8 j = 0; j < buffer[i] - '0'; j++)
+				MUST(result.push_back(block_id));
+
+			idx++;
+		}
+	}
+
+	return result;
+}
+
+i64 part1(FILE* fp)
+{
+	auto input = parse_input(fp);
+
+	usize l = 0;
+	usize r = input.size() - 1;
+
+	i64 result = 0;
+
+	while (l <= r)
+	{
+		if (input[l] != 0xFFFFFFFF)
+		{
+			result += input[l] * l;
+			l++;
+			continue;
+		}
+
+		while (l < r && input[r] == 0xFFFFFFFF)
+			r--;
+
+		if (l == r)
+			continue;
+
+		result += input[r] * l;
+		r--;
+		l++;
+	}
+
+	return result;
+}
+
+i64 part2(FILE* fp)
+{
+	auto input = parse_input(fp);
+
+	for (usize r = input.size(); r > 0;)
+	{
+		if (input[r - 1] == 0xFFFFFFFF)
+		{
+			r--;
+			continue;
+		}
+
+		const u32 id = input[r - 1];
+
+		usize rlen = 0;
+		while (r - rlen - 1 > 0 && input[r - rlen - 1] == id)
+			rlen++;
+
+		usize l = 0;
+		for (; l < r - rlen; l++)
+		{
+			if (input[l] != 0xFFFFFFFF)
+				continue;
+
+			usize llen = 1;
+			while (llen < rlen && input[l + llen] == 0xFFFFFFFF)
+				llen++;
+
+			if (llen == rlen)
+				break;
+		}
+
+		if (l < r - rlen)
+		{
+			for (usize i = 0; i < rlen; i++)
+				input[r - i - 1] = 0xFFFFFFFF;
+			for (usize i = 0; i < rlen; i++)
+				input[l + i] = id;
+		}
+
+		r -= rlen;
+		while (r > 0 && input[r - 1] == id)
+			r--;
+	}
+
+	i64 result = 0;
+	for (usize i = 0; i < input.size(); i++)
+		if (input[i] != 0xFFFFFFFF)
+			result += i * input[i];
+
+	return result;
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2024/day9_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);
+}