From 68627995f82499506f4b2f926c66da681dbda0e7 Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Tue, 19 Dec 2023 01:25:23 +0200
Subject: [PATCH] AOC2023: Implement day13

---
 userspace/aoc2023/CMakeLists.txt       |   1 +
 userspace/aoc2023/day13/CMakeLists.txt |  22 ++++
 userspace/aoc2023/day13/main.cpp       | 142 +++++++++++++++++++++++++
 3 files changed, 165 insertions(+)
 create mode 100644 userspace/aoc2023/day13/CMakeLists.txt
 create mode 100644 userspace/aoc2023/day13/main.cpp

diff --git a/userspace/aoc2023/CMakeLists.txt b/userspace/aoc2023/CMakeLists.txt
index f302eb00..19ef3082 100644
--- a/userspace/aoc2023/CMakeLists.txt
+++ b/userspace/aoc2023/CMakeLists.txt
@@ -15,6 +15,7 @@ set(AOC2023_PROJECTS
 	day10
 	day11
 	day12
+	day13
 )
 
 set(BANAN_AOC2023_BIN   ${BANAN_BIN}/aoc2023)
diff --git a/userspace/aoc2023/day13/CMakeLists.txt b/userspace/aoc2023/day13/CMakeLists.txt
new file mode 100644
index 00000000..7b39e848
--- /dev/null
+++ b/userspace/aoc2023/day13/CMakeLists.txt
@@ -0,0 +1,22 @@
+cmake_minimum_required(VERSION 3.26)
+
+project(aoc2023_day13 CXX)
+
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2023_day13 ${SOURCES})
+target_compile_options(aoc2023_day13 PUBLIC -O2 -g)
+target_link_libraries(aoc2023_day13 PUBLIC libc ban)
+
+add_dependencies(aoc2023_day13 libc-install ban-install)
+
+add_custom_target(aoc2023_day13-install
+	COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_BINARY_DIR}/aoc2023_day13 ${BANAN_AOC2023_BIN}/day13
+	DEPENDS aoc2023_day13
+	DEPENDS aoc2023_always
+)
+
+add_dependencies(aoc2023 aoc2023_day13)
+add_dependencies(aoc2023-install aoc2023_day13-install)
diff --git a/userspace/aoc2023/day13/main.cpp b/userspace/aoc2023/day13/main.cpp
new file mode 100644
index 00000000..d2afb36d
--- /dev/null
+++ b/userspace/aoc2023/day13/main.cpp
@@ -0,0 +1,142 @@
+#include <BAN/Optional.h>
+#include <BAN/String.h>
+#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 u8  = uint8_t;
+using u16 = uint16_t;
+using u32 = uint32_t;
+using u64 = uint64_t;
+
+using Grid = BAN::Vector<BAN::String>;
+
+BAN::Optional<i64> calculate_score(const Grid& grid, i64 skip_val = 0)
+{
+	// horizontal reflection
+	for (size_t x = 1; x < grid.front().size(); x++)
+	{
+		const size_t reflection_len = BAN::Math::min(x, grid.front().size() - x);
+		bool has_reflection = true;
+		for (size_t y = 0; y < grid.size() && has_reflection; y++)
+			for (size_t x_off = 0; x_off < reflection_len && has_reflection; x_off++)
+				if (grid[y][x - x_off - 1] != grid[y][x + x_off])
+					has_reflection = false;
+		if (has_reflection && (i64)x != skip_val)
+			return x;
+	}
+
+	// vertical reflection
+	for (size_t y = 1; y < grid.size(); y++)
+	{
+		const size_t reflection_len = BAN::Math::min(y, grid.size() - y);
+		bool has_reflection = true;
+		for (size_t x = 0; x < grid.front().size() && has_reflection; x++)
+			for (size_t y_off = 0; y_off < reflection_len && has_reflection; y_off++)
+				if (grid[y - y_off - 1][x] != grid[y + y_off][x])
+					has_reflection = false;
+		if (has_reflection && (i64)y * 100 != skip_val)
+			return y * 100;
+	}
+
+	return {};
+}
+
+i64 puzzle1(FILE* fp)
+{
+	i64 result = 0;
+
+	char buffer[128];
+	while (fgets(buffer, sizeof(buffer), fp))
+	{
+		Grid grid;
+		while (buffer[0] != '\n')
+		{
+			ASSERT(buffer[strlen(buffer) - 1] == '\n');
+			buffer[strlen(buffer) - 1] = '\0';
+
+			MUST(grid.emplace_back(buffer));
+
+			if (fgets(buffer, sizeof(buffer), fp) == nullptr)
+				break;
+		}
+
+		result += *calculate_score(grid);
+	}
+
+	return result;
+}
+
+i64 puzzle2(FILE* fp)
+{
+	i64 result = 0;
+
+	char buffer[128];
+	while (fgets(buffer, sizeof(buffer), fp))
+	{
+		Grid grid;
+		while (buffer[0] != '\n')
+		{
+			ASSERT(buffer[strlen(buffer) - 1] == '\n');
+			buffer[strlen(buffer) - 1] = '\0';
+
+			MUST(grid.emplace_back(buffer));
+
+			if (fgets(buffer, sizeof(buffer), fp) == nullptr)
+				break;
+		}
+
+		i64 original = *calculate_score(grid);
+
+		for (size_t y = 0; y < grid.size(); y++)
+		{
+			for (size_t x = 0; x < grid.front().size(); x++)
+			{
+				grid[y][x] = (grid[y][x] == '.') ? '#' : '.';
+				if (auto res = calculate_score(grid, original); res.has_value())
+				{
+					result += *res;
+					goto grid_done;
+				}
+				grid[y][x] = (grid[y][x] == '.') ? '#' : '.';
+			}
+		}
+
+		ASSERT_NOT_REACHED();
+
+	grid_done:
+		continue;
+	}
+
+	return result;
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2023/day13_input.txt";
+
+	if (argc >= 2)
+		file_path = argv[1];
+
+	FILE* fp = fopen(file_path, "r");
+	if (fp == nullptr)
+	{
+		perror("fopen");
+		return 1;
+	}
+
+	printf("puzzle1: %" PRId64 "\n", puzzle1(fp));
+
+	fseek(fp, 0, SEEK_SET);
+
+	printf("puzzle2: %" PRId64 "\n", puzzle2(fp));
+
+	fclose(fp);
+}