From d7b02db832ed6444ec01e0c7cd63d3a939600ede Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Thu, 5 Dec 2024 08:16:12 +0200
Subject: [PATCH] aoc2024: Implement day4 solution

---
 userspace/aoc2024/CMakeLists.txt      |   1 +
 userspace/aoc2024/day4/CMakeLists.txt |   9 ++
 userspace/aoc2024/day4/main.cpp       | 132 ++++++++++++++++++++++++++
 3 files changed, 142 insertions(+)
 create mode 100644 userspace/aoc2024/day4/CMakeLists.txt
 create mode 100644 userspace/aoc2024/day4/main.cpp

diff --git a/userspace/aoc2024/CMakeLists.txt b/userspace/aoc2024/CMakeLists.txt
index ccf5865a41..0300c63976 100644
--- a/userspace/aoc2024/CMakeLists.txt
+++ b/userspace/aoc2024/CMakeLists.txt
@@ -2,6 +2,7 @@ set(AOC2024_PROJECTS
 	day1
 	day2
 	day3
+	day4
 	full
 )
 
diff --git a/userspace/aoc2024/day4/CMakeLists.txt b/userspace/aoc2024/day4/CMakeLists.txt
new file mode 100644
index 0000000000..5d68dc987d
--- /dev/null
+++ b/userspace/aoc2024/day4/CMakeLists.txt
@@ -0,0 +1,9 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2024_day4 ${SOURCES})
+banan_include_headers(aoc2024_day4 ban)
+banan_link_library(aoc2024_day4 libc)
+
+install(TARGETS aoc2024_day4 OPTIONAL)
diff --git a/userspace/aoc2024/day4/main.cpp b/userspace/aoc2024/day4/main.cpp
new file mode 100644
index 0000000000..c4797916fd
--- /dev/null
+++ b/userspace/aoc2024/day4/main.cpp
@@ -0,0 +1,132 @@
+#include <BAN/StringView.h>
+#include <BAN/Vector.h>
+
+#include <inttypes.h>
+#include <stdio.h>
+#include <string.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;
+
+struct Grid2D
+{
+	size_t width { 0 };
+	size_t height { 0 };
+	BAN::Vector<char> data;
+};
+
+static Grid2D read_grid2d(FILE* fp)
+{
+	size_t width { 0 };
+	size_t height { 0 };
+	BAN::Vector<char> data;
+
+	char buffer[1024];
+	while (fgets(buffer, sizeof(buffer), fp))
+	{
+		const size_t len = strlen(buffer);
+		if (len == 0 || buffer[0] == '\n')
+			break;
+		if (data.empty())
+			width = len - 1;
+		height++;
+
+		ASSERT(buffer[width] == '\n');
+
+		if (data.capacity() < height * width)
+			MUST(data.reserve(2 * height * width));
+
+		MUST(data.resize(height * width));
+		memcpy(&data[(height - 1) * width], buffer, width);
+	}
+
+	(void)data.shrink_to_fit();
+
+	return Grid2D {
+		.width = width,
+		.height = height,
+		.data = BAN::move(data),
+	};
+}
+
+static bool check_match(const Grid2D& puzzle, size_t x, size_t y, i32 step_x, i32 step_y, BAN::StringView target)
+{
+	if (i32 ex = (i32)x + step_x * (i32)(target.size() - 1); ex < 0 || ex >= (i32)puzzle.width)
+		return false;
+	if (i32 ey = (i32)y + step_y * (i32)(target.size() - 1); ey < 0 || ey >= (i32)puzzle.height)
+		return false;
+	for (size_t i = 0; i < target.size(); i++)
+		if (target[i] != puzzle.data[(y + i * step_y) * puzzle.width + (x + i * step_x)])
+			return false;
+	return true;
+}
+
+i64 part1(FILE* fp)
+{
+	i64 result = 0;
+
+	auto puzzle = read_grid2d(fp);
+	for (size_t y = 0; y < puzzle.height; y++) {
+		for (size_t x = 0; x < puzzle.width; x++) {
+			result += check_match(puzzle, x, y, 1,  0, "XMAS"_sv);
+			result += check_match(puzzle, x, y, 0,  1, "XMAS"_sv);
+			result += check_match(puzzle, x, y, 1,  1, "XMAS"_sv);
+			result += check_match(puzzle, x, y, 1, -1, "XMAS"_sv);
+
+			result += check_match(puzzle, x, y, 1,  0, "SAMX"_sv);
+			result += check_match(puzzle, x, y, 0,  1, "SAMX"_sv);
+			result += check_match(puzzle, x, y, 1,  1, "SAMX"_sv);
+			result += check_match(puzzle, x, y, 1, -1, "SAMX"_sv);
+		}
+	}
+
+	return result;
+}
+
+i64 part2(FILE* fp)
+{
+	i64 result = 0;
+
+	auto puzzle = read_grid2d(fp);
+	for (size_t y = 1; y < puzzle.height - 1; y++) {
+		for (size_t x = 1; x < puzzle.width - 1; x++) {
+			if (!check_match(puzzle, x - 1, y - 1, 1,  1, "MAS") && !check_match(puzzle, x - 1, y - 1, 1,  1, "SAM"))
+				continue;
+			if (!check_match(puzzle, x - 1, y + 1, 1, -1, "MAS") && !check_match(puzzle, x - 1, y + 1, 1, -1, "SAM"))
+				continue;
+			result++;
+		}
+	}
+
+	return result;
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2024/day4_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);
+}