From 2e39668605c5c26189732bdd9316d3a36eeb0fc4 Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Wed, 18 Dec 2024 14:00:22 +0200
Subject: [PATCH] aoc2024: Implement day18 solution

---
 userspace/aoc2024/CMakeLists.txt       |   1 +
 userspace/aoc2024/day18/CMakeLists.txt |   9 ++
 userspace/aoc2024/day18/main.cpp       | 125 +++++++++++++++++++++++++
 3 files changed, 135 insertions(+)
 create mode 100644 userspace/aoc2024/day18/CMakeLists.txt
 create mode 100644 userspace/aoc2024/day18/main.cpp

diff --git a/userspace/aoc2024/CMakeLists.txt b/userspace/aoc2024/CMakeLists.txt
index d5065881..e0329a37 100644
--- a/userspace/aoc2024/CMakeLists.txt
+++ b/userspace/aoc2024/CMakeLists.txt
@@ -16,6 +16,7 @@ set(AOC2024_PROJECTS
 	day15
 	day16
 	day17
+	day18
 	full
 )
 
diff --git a/userspace/aoc2024/day18/CMakeLists.txt b/userspace/aoc2024/day18/CMakeLists.txt
new file mode 100644
index 00000000..4231ab64
--- /dev/null
+++ b/userspace/aoc2024/day18/CMakeLists.txt
@@ -0,0 +1,9 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2024_day18 ${SOURCES})
+banan_include_headers(aoc2024_day18 ban)
+banan_link_library(aoc2024_day18 libc)
+
+install(TARGETS aoc2024_day18 OPTIONAL)
diff --git a/userspace/aoc2024/day18/main.cpp b/userspace/aoc2024/day18/main.cpp
new file mode 100644
index 00000000..5b174186
--- /dev/null
+++ b/userspace/aoc2024/day18/main.cpp
@@ -0,0 +1,125 @@
+#include <BAN/Array.h>
+#include <BAN/String.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 isize = ssize_t;
+
+using u8  = uint8_t;
+using u16 = uint16_t;
+using u32 = uint32_t;
+using u64 = uint64_t;
+using usize = size_t;
+
+template<typename T>
+struct Vec2
+{
+	T x, y;
+};
+
+template<usize W, usize H>
+static BAN::Optional<usize> steps_to_finnish(BAN::Array<BAN::Array<bool, W>, H>& map)
+{
+	BAN::Vector<Vec2<usize>> pending;
+	MUST(pending.push_back({ 0, 0 }));
+
+	for (usize step = 0;; step++)
+	{
+		BAN::Vector<Vec2<usize>> next;
+		for (auto pos : pending)
+		{
+			if (map[pos.y][pos.x])
+				continue;
+			map[pos.y][pos.x] = true;
+
+			if (pos.x == W - 1 && pos.y == H - 1)
+				return step;
+
+			if (pos.y > 0     && !map[pos.y - 1][pos.x    ]) MUST(next.push_back({ pos.x,     pos.y - 1 }));
+			if (pos.x > 0     && !map[pos.y    ][pos.x - 1]) MUST(next.push_back({ pos.x - 1, pos.y     }));
+			if (pos.y < H - 1 && !map[pos.y + 1][pos.x    ]) MUST(next.push_back({ pos.x,     pos.y + 1 }));
+			if (pos.x < W - 1 && !map[pos.y    ][pos.x + 1]) MUST(next.push_back({ pos.x + 1, pos.y     }));
+		}
+
+		if (next.empty())
+			break;
+		pending = BAN::move(next);
+	}
+
+	return {};
+}
+
+i64 part1(FILE* fp)
+{
+	BAN::Array<BAN::Array<bool, 71>, 71> map(false);
+	for (usize i = 0; i < 1024; i++)
+	{
+		usize x, y;
+		ASSERT(fscanf(fp, "%zu,%zu\n", &x, &y) == 2);
+		map[y][x] = true;
+	}
+
+	return steps_to_finnish(map).value();
+}
+
+BAN::String part2(FILE* fp)
+{
+	BAN::Vector<Vec2<usize>> bytes;
+	for (;;)
+	{
+		usize x, y;
+		if (fscanf(fp, "%zu,%zu\n", &x, &y) != 2)
+			break;
+		MUST(bytes.push_back({ x, y }));
+	}
+
+	usize l = 0;
+	usize r = bytes.size() - 1;
+
+	while (l <= r)
+	{
+		const usize mid = l + (r - l) / 2;
+
+		BAN::Array<BAN::Array<bool, 71>, 71> map(false);
+		for (usize i = 0; i <= mid; i++)
+			map[bytes[i].y][bytes[i].x] = true;
+
+		if (steps_to_finnish(map).has_value())
+			l = mid + 1;
+		else if (l == mid)
+			return MUST(BAN::String::formatted("{},{}", bytes[mid].x, bytes[mid].y));
+		else
+			r = mid;
+	}
+
+	ASSERT_NOT_REACHED();
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2024/day18_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: %s\n", part2(fp).data());
+
+	fclose(fp);
+}