From 531211e09daea3ccd5e88c91bbbbbed93920219a Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Wed, 6 Dec 2023 07:27:25 +0200
Subject: [PATCH] AOC2023: implement day6

---
 userspace/aoc2023/CMakeLists.txt      |   1 +
 userspace/aoc2023/day6/CMakeLists.txt |  22 +++++
 userspace/aoc2023/day6/main.cpp       | 122 ++++++++++++++++++++++++++
 3 files changed, 145 insertions(+)
 create mode 100644 userspace/aoc2023/day6/CMakeLists.txt
 create mode 100644 userspace/aoc2023/day6/main.cpp

diff --git a/userspace/aoc2023/CMakeLists.txt b/userspace/aoc2023/CMakeLists.txt
index 81b74da6c1..3a44bc67fc 100644
--- a/userspace/aoc2023/CMakeLists.txt
+++ b/userspace/aoc2023/CMakeLists.txt
@@ -8,6 +8,7 @@ set(AOC2023_PROJECTS
 	day3
 	day4
 	day5
+	day6
 )
 
 set(BANAN_AOC2023_BIN   ${BANAN_BIN}/aoc2023)
diff --git a/userspace/aoc2023/day6/CMakeLists.txt b/userspace/aoc2023/day6/CMakeLists.txt
new file mode 100644
index 0000000000..c1e5eb5e4c
--- /dev/null
+++ b/userspace/aoc2023/day6/CMakeLists.txt
@@ -0,0 +1,22 @@
+cmake_minimum_required(VERSION 3.26)
+
+project(aoc2023_day6 CXX)
+
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2023_day6 ${SOURCES})
+target_compile_options(aoc2023_day6 PUBLIC -O2 -g)
+target_link_libraries(aoc2023_day6 PUBLIC libc ban)
+
+add_dependencies(aoc2023_day6 libc-install ban-install)
+
+add_custom_target(aoc2023_day6-install
+	COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_BINARY_DIR}/aoc2023_day6 ${BANAN_AOC2023_BIN}/day6
+	DEPENDS aoc2023_day6
+	DEPENDS aoc2023_always
+)
+
+add_dependencies(aoc2023 aoc2023_day6)
+add_dependencies(aoc2023-install aoc2023_day6-install)
diff --git a/userspace/aoc2023/day6/main.cpp b/userspace/aoc2023/day6/main.cpp
new file mode 100644
index 0000000000..b857fc51af
--- /dev/null
+++ b/userspace/aoc2023/day6/main.cpp
@@ -0,0 +1,122 @@
+#include <BAN/Vector.h>
+
+#include <ctype.h>
+#include <stdio.h>
+#include <stdint.h>
+
+using i64 = int64_t;
+
+i64 parse_i64_all_digits(BAN::StringView part)
+{
+	i64 result = 0;
+	for (char c : part)
+		if (isdigit(c))
+			result = (result * 10) + (c - '0');
+	return result;
+}
+
+i64 puzzle1(FILE* fp)
+{
+	BAN::Vector<i64> times, distances;
+
+	{
+		char buffer[128];
+		fgets(buffer, sizeof(buffer), fp);
+		BAN::StringView line(buffer);
+		line = line.substring(10);
+		line = line.substring(0, line.size() - 1);
+
+		auto split = MUST(line.split(' '));
+		for (auto part : split)
+			MUST(times.push_back(parse_i64_all_digits(part)));
+	}
+
+	{
+		char buffer[128];
+		fgets(buffer, sizeof(buffer), fp);
+		BAN::StringView line(buffer);
+		line = line.substring(10);
+		line = line.substring(0, line.size() - 1);
+
+		auto split = MUST(line.split(' '));
+		for (auto part : split)
+			MUST(distances.push_back(parse_i64_all_digits(part)));
+	}
+
+	ASSERT(times.size() == distances.size());
+
+	i64 result = 1;
+
+	for (size_t i = 0; i < times.size(); i++)
+	{
+		i64 time = times[i];
+		i64 distance = distances[i];
+
+		i64 min = distance / time - 1;
+		while ((time - min) * min <= distance)
+			min++;
+
+		i64 max = min;
+		while ((time - max) * max > distance)
+			max++;
+
+		result *= max - min;
+	}
+
+	return result;
+}
+
+i64 puzzle2(FILE* fp)
+{
+	i64 time = 0;
+	i64 distance = 0;
+
+	{
+		char buffer[128];
+		fgets(buffer, sizeof(buffer), fp);
+		BAN::StringView line(buffer);
+		line = line.substring(10);
+		time = parse_i64_all_digits(line);
+	}
+
+	{
+		char buffer[128];
+		fgets(buffer, sizeof(buffer), fp);
+		BAN::StringView line(buffer);
+		line = line.substring(10);
+		distance = parse_i64_all_digits(line);
+	}
+
+	i64 min = distance / time - 1;
+	while ((time - min) * min <= distance)
+		min++;
+
+	i64 max = min;
+	while ((time - max) * max > distance)
+		max++;
+
+	return max - min;
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2023/day6_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);
+}