From a231f8587e514a89ea7b9099909749e6fe3d1f78 Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Mon, 2 Dec 2024 20:12:52 +0200
Subject: [PATCH] aoc2024: Implement day2 solution

---
 userspace/aoc2024/CMakeLists.txt      |   1 +
 userspace/aoc2024/day2/CMakeLists.txt |   9 ++
 userspace/aoc2024/day2/main.cpp       | 118 ++++++++++++++++++++++++++
 3 files changed, 128 insertions(+)
 create mode 100644 userspace/aoc2024/day2/CMakeLists.txt
 create mode 100644 userspace/aoc2024/day2/main.cpp

diff --git a/userspace/aoc2024/CMakeLists.txt b/userspace/aoc2024/CMakeLists.txt
index dde0c76b3f..ed25e16121 100644
--- a/userspace/aoc2024/CMakeLists.txt
+++ b/userspace/aoc2024/CMakeLists.txt
@@ -1,5 +1,6 @@
 set(AOC2024_PROJECTS
 	day1
+	day2
 	full
 )
 
diff --git a/userspace/aoc2024/day2/CMakeLists.txt b/userspace/aoc2024/day2/CMakeLists.txt
new file mode 100644
index 0000000000..a679325f89
--- /dev/null
+++ b/userspace/aoc2024/day2/CMakeLists.txt
@@ -0,0 +1,9 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2024_day2 ${SOURCES})
+banan_include_headers(aoc2024_day2 ban)
+banan_link_library(aoc2024_day2 libc)
+
+install(TARGETS aoc2024_day2 OPTIONAL)
diff --git a/userspace/aoc2024/day2/main.cpp b/userspace/aoc2024/day2/main.cpp
new file mode 100644
index 0000000000..751f17c451
--- /dev/null
+++ b/userspace/aoc2024/day2/main.cpp
@@ -0,0 +1,118 @@
+#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;
+
+bool is_safe(i64 curr, i64 prev, bool inc)
+{
+	i64 abs_diff = BAN::Math::abs(curr - prev);
+	if (abs_diff == 0 || abs_diff > 3)
+		return false;
+	if ((curr > prev) != inc)
+		return false;
+	return true;
+}
+
+i64 part1(FILE* fp)
+{
+	i64 ret = 0;
+
+	char buffer[128];
+	while (fgets(buffer, sizeof(buffer), fp))
+	{
+		auto strs = MUST(BAN::StringView(buffer).split(' '));
+		ASSERT(strs.size() >= 2);
+
+		i64 prev = atoll(strs[0].data());
+		i64 curr = atoll(strs[1].data());
+
+		const bool inc = (curr > prev);
+		if (!is_safe(curr, prev, inc))
+			continue;
+
+		bool safe = true;
+		for (size_t i = 2; i < strs.size() && safe; i++)
+		{
+			prev = curr;
+			curr = atoll(strs[i].data());
+			safe = is_safe(curr, prev, inc);
+		}
+
+		ret += safe;
+	}
+
+	return ret;
+}
+
+i64 part2(FILE* fp)
+{
+	i64 ret = 0;
+
+	char buffer[128];
+	while (fgets(buffer, sizeof(buffer), fp))
+	{
+		auto strs = MUST(BAN::StringView(buffer).split(' '));
+		ASSERT(strs.size() >= 3);
+
+		for (size_t skip_idx = 0; skip_idx < strs.size(); skip_idx++)
+		{
+			i64 prev = atoll(strs[0 + (skip_idx <= 0)].data());
+			i64 curr = atoll(strs[1 + (skip_idx <= 1)].data());
+
+			const bool inc = (curr > prev);
+			if (!is_safe(curr, prev, inc))
+				continue;
+
+			bool safe = true;
+			for (size_t i = 2 + (skip_idx <= 2); i < strs.size() && safe; i++)
+			{
+				if (i == skip_idx)
+					continue;
+				prev = curr;
+				curr = atoll(strs[i].data());
+				safe = is_safe(curr, prev, inc);
+			}
+			if (!safe)
+				continue;
+
+			ret++;
+			break;
+		}
+	}
+
+	return ret;
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2024/day2_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);
+}