aoc2025: Implement day7 solution

userspace/aoc2025/CMakeLists.txt

@@ -5,6 +5,7 @@ set(AOC2025_PROJECTS
 	day4
 	day5
 	day6
+	day7
 	full
 )
 

userspace/aoc2025/day7/CMakeLists.txt

@@ -0,0 +1,9 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2025_day7 ${SOURCES})
+banan_include_headers(aoc2025_day7 ban)
+banan_link_library(aoc2025_day7 libc)
+
+install(TARGETS aoc2025_day7 OPTIONAL)

userspace/aoc2025/day7/main.cpp

@@ -0,0 +1,131 @@
+#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 u8  = uint8_t;
+using u16 = uint16_t;
+using u32 = uint32_t;
+using u64 = uint64_t;
+
+static BAN::Vector<BAN::String> parse_lines(FILE* fp)
+{
+	BAN::Vector<BAN::String> lines;
+	MUST(lines.emplace_back());
+
+	char line_buffer[128];
+	while (fgets(line_buffer, sizeof(line_buffer), fp))
+	{
+		MUST(lines.back().append(line_buffer));
+		if (lines.back().back() != '\n')
+			continue;
+		lines.back().pop_back();
+		MUST(lines.emplace_back());
+	}
+
+	while (lines.back().empty())
+		lines.pop_back();
+
+	return lines;
+}
+
+i64 part1(FILE* fp)
+{
+	i32 result = 0;
+
+	auto lines = parse_lines(fp);
+
+	for (char& ch : lines.front())
+		if (ch == 'S')
+			ch = '|';
+
+	for (size_t y = 0; y < lines.size() - 1; y++)
+	{
+		for (size_t x = 0; x < lines[y].size(); x++)
+		{
+			if (lines[y][x] != '|')
+				continue;
+
+			switch (lines[y + 1][x])
+			{
+				case '.':
+					lines[y + 1][x] = '|';
+					break;
+				case '^':
+					lines[y + 1][x - 1] = '|';
+					lines[y + 1][x + 1] = '|';
+					result++;
+					break;
+			}
+		}
+	}
+
+	return result;
+}
+
+i64 part2(FILE* fp)
+{
+	auto lines = parse_lines(fp);
+
+	const size_t h = lines.size();
+	const size_t w = lines.front().size();
+
+	BAN::Vector<i64> timelines;
+	MUST(timelines.resize(w * h));
+
+	const auto get_char_value = [](char ch) { return ch == '.' ? 0 : ch == 'S' ? 1 : -1; };
+	for (size_t y = 0; y < h; y++)
+		for (size_t x = 0; x < w; x++)
+			timelines[y * w + x] = get_char_value(lines[y][x]);
+
+	for (size_t y = 1; y < h; y++)
+	{
+		for (size_t x = 0; x < w; x++)
+		{
+			if (timelines[(y - 1) * w + x] < 0)
+				;
+			else if (timelines[y * w + x] >= 0)
+				timelines[y * w + x] += timelines[(y - 1) * w + x];
+			else
+			{
+				timelines[y * w + x - 1] += timelines[(y - 1) * w + x];
+				timelines[y * w + x + 1] += timelines[(y - 1) * w + x];
+			}
+		}
+	}
+
+	i64 result = 0;
+	for (size_t x = 0; x < w; x++)
+		if (auto value = timelines[(h - 1) * w + x]; value > 0)
+			result += value;
+	return result;
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2025/day7_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);
+}