AOC2023: Implement day8

Second part was kinda weird. You are supposted to assume something
of the input, which necessarily is not true.

userspace/aoc2023/CMakeLists.txt

@@ -10,6 +10,7 @@ set(AOC2023_PROJECTS
 	day5
 	day6
 	day7
+	day8
 )
 
 set(BANAN_AOC2023_BIN   ${BANAN_BIN}/aoc2023)

userspace/aoc2023/day8/CMakeLists.txt

@@ -0,0 +1,22 @@
+cmake_minimum_required(VERSION 3.26)
+
+project(aoc2023_day8 CXX)
+
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2023_day8 ${SOURCES})
+target_compile_options(aoc2023_day8 PUBLIC -O2 -g)
+target_link_libraries(aoc2023_day8 PUBLIC libc ban)
+
+add_dependencies(aoc2023_day8 libc-install ban-install)
+
+add_custom_target(aoc2023_day8-install
+	COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_BINARY_DIR}/aoc2023_day8 ${BANAN_AOC2023_BIN}/day8
+	DEPENDS aoc2023_day8
+	DEPENDS aoc2023_always
+)
+
+add_dependencies(aoc2023 aoc2023_day8)
+add_dependencies(aoc2023-install aoc2023_day8-install)

userspace/aoc2023/day8/main.cpp

@@ -0,0 +1,131 @@
+#include <BAN/HashMap.h>
+#include <BAN/String.h>
+
+#include <ctype.h>
+#include <stdio.h>
+#include <stdint.h>
+
+using i32 = int32_t;
+using i64 = int64_t;
+
+using u32 = uint32_t;
+using u64 = uint64_t;
+
+static u32 coord_to_u32(BAN::StringView coord)
+{
+	ASSERT(coord.size() == 3);
+	return ((u32)coord[2] << 16) | ((u32)coord[1] << 8) | (u32)coord[0];
+}
+
+i64 puzzle1(FILE* fp)
+{
+	BAN::HashMap<u32, u32[2]> targets;
+	BAN::String left_right_path;
+
+	{
+		char buffer[512];
+		if (!fgets(buffer, sizeof(buffer), fp))
+			return -1;
+		MUST(left_right_path.append(buffer));
+		left_right_path.pop_back();
+
+		if (!fgets(buffer, sizeof(buffer), fp))
+			return -1;
+		while (fgets(buffer, sizeof(buffer), fp))
+		{
+			BAN::StringView line(buffer);
+			if (line.size() < 15)
+				continue;
+			MUST(targets.emplace(
+				coord_to_u32(line.substring(0, 3)),
+				coord_to_u32(line.substring(7, 3)),
+				coord_to_u32(line.substring(12, 3))
+			));
+		}
+	}
+
+	u32 current = coord_to_u32("AAA"sv);
+	u32 target = coord_to_u32("ZZZ"sv);
+
+	i64 steps = 0;
+	for (; current != target; steps++)
+	{
+		char direction = left_right_path[steps % left_right_path.size()];
+		current = targets[current][direction == 'R'];
+	}
+
+	return steps;
+}
+
+i64 puzzle2(FILE* fp)
+{
+	BAN::HashMap<u32, u32[2]> targets;
+	BAN::String left_right_path;
+
+	{
+		char buffer[512];
+		if (!fgets(buffer, sizeof(buffer), fp))
+			return -1;
+		MUST(left_right_path.append(buffer));
+		left_right_path.pop_back();
+
+		if (!fgets(buffer, sizeof(buffer), fp))
+			return -1;
+		while (fgets(buffer, sizeof(buffer), fp))
+		{
+			BAN::StringView line(buffer);
+			if (line.size() < 15)
+				continue;
+			MUST(targets.emplace(
+				coord_to_u32(line.substring(0, 3)),
+				coord_to_u32(line.substring(7, 3)),
+				coord_to_u32(line.substring(12, 3))
+			));
+		}
+	}
+
+	i64 result = 1;
+	for (auto [key, _] : targets)
+	{
+		if ((key >> 16) != 'A')
+			continue;
+
+		i64 steps = 0;
+		for (u32 pos = key; (pos >> 16) != 'Z'; steps++)
+		{
+			char direction = left_right_path[steps % left_right_path.size()];
+			pos = targets[pos][direction == 'R'];
+		}
+
+		// Calculating LCM of all steps only works if steps is a multiple of full path size.
+		// This seems to be the case with my input, but it's good to verify...
+		ASSERT(steps % left_right_path.size() == 0);
+
+		result = BAN::Math::lcm(result, steps);
+	}
+
+	return result;
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2023/day8_input.txt";
+
+	if (argc >= 2)
+		file_path = argv[1];
+
+	FILE* fp = fopen(file_path, "r");
+	if (fp == nullptr)
+	{
+		perror("fopen");
+		return 1;
+	}
+
+	printf("puzzle1: %lld\n", puzzle1(fp));
+
+	fseek(fp, 0, SEEK_SET);
+
+	printf("puzzle2: %lld\n", puzzle2(fp));
+
+	fclose(fp);
+}