aoc2024: Implement day21 solution

userspace/aoc2024/CMakeLists.txt

@@ -19,6 +19,7 @@ set(AOC2024_PROJECTS
 	day18
 	day19
 	day20
+	day21
 	full
 )
 

userspace/aoc2024/day21/CMakeLists.txt

@@ -0,0 +1,9 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2024_day21 ${SOURCES})
+banan_include_headers(aoc2024_day21 ban)
+banan_link_library(aoc2024_day21 libc)
+
+install(TARGETS aoc2024_day21 OPTIONAL)

userspace/aoc2024/day21/main.cpp

@@ -0,0 +1,254 @@
+#include <BAN/Array.h>
+#include <BAN/HashMap.h>
+#include <BAN/Vector.h>
+#include <BAN/StringView.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;
+
+BAN::Vector<BAN::Vector<char>> parse_input(FILE* fp)
+{
+	BAN::Vector<BAN::Vector<char>> result;
+
+	char buffer[8];
+	while (fgets(buffer, sizeof(buffer), fp))
+	{
+		if (buffer[0] == '\n')
+			break;
+		ASSERT(buffer[4] == '\n');
+
+		MUST(result.emplace_back());
+		MUST(result.back().resize(4));
+		memcpy(result.back().data(), buffer, 4);
+	}
+
+	return result;
+}
+
+struct Vec2
+{
+	i32 x, y;
+};
+
+static constexpr Vec2 position_numeric(char c)
+{
+	/*
+		7 8 9
+		4 5 6
+		1 2 3
+		. 0 A
+	*/
+
+	switch (c)
+	{
+		case '0': return { 1, 0 };
+		case 'A': return { 2, 0 };
+		case '1': return { 0, 1 };
+		case '2': return { 1, 1 };
+		case '3': return { 2, 1 };
+		case '4': return { 0, 2 };
+		case '5': return { 1, 2 };
+		case '6': return { 2, 2 };
+		case '7': return { 0, 3 };
+		case '8': return { 1, 3 };
+		case '9': return { 2, 3 };
+	}
+
+	ASSERT_NOT_REACHED();
+}
+
+static constexpr Vec2 position_directional(char c)
+{
+	/*
+		. ^ A
+		< v >
+	*/
+
+	switch (c)
+	{
+		case '<': return { 0, -1 };
+		case 'v': return { 1, -1 };
+		case '>': return { 2, -1 };
+		case '^': return { 1,  0 };
+		case 'A': return { 2,  0 };
+	}
+
+	ASSERT_NOT_REACHED();
+}
+
+struct Key
+{
+	Vec2 s;
+	Vec2 e;
+	u64 presses;
+	u64 max_depth;
+
+	constexpr bool operator==(const Key& other) const
+	{
+		return
+			s.x       == other.s.x &&
+			s.y       == other.s.y &&
+			e.x       == other.e.x &&
+			e.y       == other.e.y &&
+			presses   == other.presses &&
+			max_depth == other.max_depth;
+	}
+};
+
+struct KeyHash
+{
+	constexpr BAN::hash_t operator()(const Key& key) const
+	{
+		return
+			BAN::hash<i32>()(key.s.x) ^
+			BAN::hash<i32>()(key.s.y) ^
+			BAN::hash<i32>()(key.e.x) ^
+			BAN::hash<i32>()(key.e.y) ^
+			BAN::hash<u64>()(key.presses) ^
+			BAN::hash<u64>()(key.max_depth);
+	}
+};
+
+static BAN::HashMap<Key, u64, KeyHash> s_cache;
+
+static constexpr u64 recurse(Vec2 s, Vec2 e, u64 presses, u32 max_depth)
+{
+	using BAN::Math::abs;
+
+	if (max_depth == 0)
+		return presses;
+
+	const auto cache_key = Key {
+		s, e, presses, max_depth
+	};
+
+	auto it = s_cache.find(cache_key);
+	if (it != s_cache.end())
+		return it->value;
+
+	const auto diff = Vec2 {
+		.x = e.x - s.x,
+		.y = e.y - s.y,
+	};
+
+	u64 result = 0;
+
+	if (diff.x == 0)
+	{
+		const auto t_pos = position_directional(diff.y > 0 ? '^' : 'v');
+		const auto a_pos = position_directional('A');
+		result += recurse(a_pos, t_pos, abs(diff.y), max_depth - 1);
+		result += recurse(t_pos, a_pos, presses,     max_depth - 1);
+	}
+	else if (diff.y == 0)
+	{
+		const auto t_pos = position_directional(diff.x > 0 ? '>' : '<');
+		const auto a_pos = position_directional('A');
+		result += recurse(a_pos, t_pos, abs(diff.x), max_depth - 1);
+		result += recurse(t_pos, a_pos, presses,     max_depth - 1);
+	}
+	else if (s.y == 0 && e.x == 0)
+	{
+		const auto t1_pos = position_directional(diff.y > 0 ? '^' : 'v');
+		const auto t2_pos = position_directional(diff.x > 0 ? '>' : '<');
+		const auto a_pos = position_directional('A');
+		result += recurse(a_pos,  t1_pos, abs(diff.y), max_depth - 1);
+		result += recurse(t1_pos, t2_pos, abs(diff.x), max_depth - 1);
+		result += recurse(t2_pos, a_pos,  presses,     max_depth - 1);
+	}
+	else if ((s.x == 0 && e.y == 0) || diff.x < 0)
+	{
+		const auto t1_pos = position_directional(diff.x > 0 ? '>' : '<');
+		const auto t2_pos = position_directional(diff.y > 0 ? '^' : 'v');
+		const auto a_pos = position_directional('A');
+		result += recurse(a_pos,  t1_pos, abs(diff.x), max_depth - 1);
+		result += recurse(t1_pos, t2_pos, abs(diff.y), max_depth - 1);
+		result += recurse(t2_pos, a_pos,  presses,     max_depth - 1);
+	}
+	else
+	{
+		const auto t1_pos = position_directional(diff.y > 0 ? '^' : 'v');
+		const auto t2_pos = position_directional(diff.x > 0 ? '>' : '<');
+		const auto a_pos = position_directional('A');
+		result += recurse(a_pos,  t1_pos, abs(diff.y), max_depth - 1);
+		result += recurse(t1_pos, t2_pos, abs(diff.x), max_depth - 1);
+		result += recurse(t2_pos, a_pos,  presses,     max_depth - 1);
+	}
+
+	MUST(s_cache.insert(cache_key, result));
+
+	return result;
+}
+
+i64 part1(FILE* fp)
+{
+	auto input = parse_input(fp);
+
+	u64 result = 0;
+	for (auto code : input)
+	{
+		u64 length = 0;
+		for (usize i = 0; i < code.size(); i++)
+		{
+			const auto s_pos = position_numeric(i ? code[i - 1] : 'A');
+			const auto e_pos = position_numeric(code[i]);
+			length += recurse(s_pos, e_pos, 1, 3);
+		}
+		result += length * atoi(code.data());
+	}
+	return result;
+}
+
+i64 part2(FILE* fp)
+{
+	auto input = parse_input(fp);
+
+	u64 result = 0;
+	for (auto code : input)
+	{
+		u64 length = 0;
+		for (usize i = 0; i < code.size(); i++)
+		{
+			const auto s_pos = position_numeric(i ? code[i - 1] : 'A');
+			const auto e_pos = position_numeric(code[i]);
+			length += recurse(s_pos, e_pos, 1, 26);
+		}
+		result += length * atoi(code.data());
+	}
+	return result;
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2024/day21_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);
+}