aoc2025: Implement day8 solution

userspace/aoc2025/CMakeLists.txt

@@ -6,6 +6,7 @@ set(AOC2025_PROJECTS
 	day5
 	day6
 	day7
+	day8
 	full
 )
 

userspace/aoc2025/day8/CMakeLists.txt

@@ -0,0 +1,9 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2025_day8 ${SOURCES})
+banan_include_headers(aoc2025_day8 ban)
+banan_link_library(aoc2025_day8 libc)
+
+install(TARGETS aoc2025_day8 OPTIONAL)

userspace/aoc2025/day8/main.cpp

@@ -0,0 +1,179 @@
+#include <BAN/HashSet.h>
+#include <BAN/Heap.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;
+
+struct Point
+{
+	i64 x, y, z;
+
+	constexpr bool operator==(const Point& other) const
+	{
+		return x == other.x && y == other.y && z == other.z;
+	}
+};
+
+static BAN::Vector<Point> parse_points(FILE* fp)
+{
+	BAN::Vector<Point> points;
+
+	i64 x, y, z;
+	while (fscanf(fp, "%" SCNi64 ",%" SCNi64 ",%" SCNi64, &x, &y, &z) == 3)
+		MUST(points.emplace_back(x, y, z));
+
+	return points;
+}
+
+struct PointPair
+{
+	Point a, b;
+
+	constexpr i64 dist() const
+	{
+		return (a.x - b.x) * (a.x - b.x)
+		     + (a.y - b.y) * (a.y - b.y)
+		     + (a.z - b.z) * (a.z - b.z);
+	}
+
+	constexpr bool operator>(const PointPair& other) const
+	{
+		return dist() > other.dist();
+	}
+};
+
+static BAN::Vector<PointPair> build_point_pair_heap(const BAN::Vector<Point>& points)
+{
+	BAN::Vector<PointPair> pairs;
+	MUST(pairs.reserve(points.size() * (points.size() + 1) / 2));
+
+	for (size_t i = 0; i < points.size(); i++)
+		for (size_t j = i + 1; j < points.size(); j++)
+			MUST(pairs.push_back({ points[i], points[j] }));
+
+	BAN::make_heap(pairs.begin(), pairs.end(), BAN::greater<PointPair> {});
+
+	return pairs;
+}
+
+using Circuit = BAN::Vector<Point>;
+
+static BAN::Vector<Circuit> build_circuits(const BAN::Vector<Point>& points)
+{
+	BAN::Vector<Circuit> circuits;
+	MUST(circuits.reserve(points.size()));
+
+	for (size_t i = 0; i < points.size(); i++)
+		MUST(circuits.emplace_back(1, points[i]));
+
+	return circuits;
+}
+
+static void combine_circuits_with_points(BAN::Vector<Circuit>& circuits, const Point& a, const Point& b)
+{
+	size_t a_index = SIZE_MAX;
+	size_t b_index = SIZE_MAX;
+
+	for (size_t i = 0; i < circuits.size(); i++)
+	{
+		if (circuits[i].contains(a))
+			a_index = i;
+		if (circuits[i].contains(b))
+			b_index = i;
+	}
+
+	if (a_index == b_index)
+		return;
+
+	MUST(circuits[a_index].reserve(circuits[a_index].size() + circuits[b_index].size()));
+	for (auto point : circuits[b_index])
+		MUST(circuits[a_index].push_back(point));
+
+	circuits.remove(b_index);
+}
+
+i64 part1(FILE* fp)
+{
+	auto points = parse_points(fp);
+	auto pairs = build_point_pair_heap(points);
+	auto circuits = build_circuits(points);
+
+	for (size_t i = 0; i < 1000; i++)
+	{
+		const auto [a, b] = pairs.front();
+		BAN::pop_heap(pairs.begin(), pairs.end() - i, BAN::greater<PointPair> {});
+
+		combine_circuits_with_points(circuits, a, b);
+	}
+
+	const auto size_comp =
+		[](const auto& a, const auto& b)
+		{
+			return a.size() < b.size();
+		};
+
+	BAN::make_heap(circuits.begin(), circuits.end(), size_comp);
+
+	i64 result = 1;
+
+	for (size_t i = 0; i < 3; i++)
+	{
+		result *= circuits.front().size();
+		BAN::pop_heap(circuits.begin(), circuits.end() - i, size_comp);
+	}
+
+	return result;
+}
+
+i64 part2(FILE* fp)
+{
+	auto points = parse_points(fp);
+	auto pairs = build_point_pair_heap(points);
+	auto circuits = build_circuits(points);
+
+	for (size_t i = 0; i < pairs.size(); i++)
+	{
+		const auto [a, b] = pairs.front();
+		BAN::pop_heap(pairs.begin(), pairs.end() - i, BAN::greater<PointPair> {});
+
+		combine_circuits_with_points(circuits, a, b);
+		if (circuits.size() == 1)
+			return a.x * b.x;
+	}
+
+	ASSERT_NOT_REACHED();
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2025/day8_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);
+}