aoc2024: Implement day13 solution

userspace/aoc2024/CMakeLists.txt

@@ -11,6 +11,7 @@ set(AOC2024_PROJECTS
 	day10
 	day11
 	day12
+	day13
 	full
 )
 

userspace/aoc2024/day13/CMakeLists.txt

@@ -0,0 +1,9 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(aoc2024_day13 ${SOURCES})
+banan_include_headers(aoc2024_day13 ban)
+banan_link_library(aoc2024_day13 libc)
+
+install(TARGETS aoc2024_day13 OPTIONAL)

userspace/aoc2024/day13/main.cpp

@@ -0,0 +1,115 @@
+#include <BAN/Assert.h>
+#include <BAN/Math.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;
+using usize = size_t;
+
+struct vec_t { i64 x, y; };
+
+u64 fewest_tokens(vec_t a, vec_t b, vec_t p)
+{
+	ASSERT(a.x * b.y != b.x * a.y);
+
+	// n * a.x + m * b.x = p.x  <==>  m = (p.x - n * a.x) / b.x
+	// n * a.y + m * b.y = p.y
+
+	// n * a.y + ((p.x - n * a.x) / b.x) * b.y = p.y
+	// => n * a.y + (p.x / b.x - n * a.x / b.x) * b.y = p.y
+	// => n * a.y + p.x / b.x * b.y - n * a.x / b.x * b.y = p.y
+	// => n * a.y - n * a.x / b.x * b.y = p.y - p.x / b.x * b.y
+	// => n * a.y * b.x - n * a.x * b.y = p.y * b.x - p.x * b.y
+	// => n * (a.y * b.x - a.x * b.y) = p.y * b.x - p.x * b.y
+	// => n = (p.y * b.x - p.x * b.y) / (a.y * b.x - a.x * b.y)
+
+	const i64 n_num = p.y * b.x - p.x * b.y;
+	const i64 n_den = a.y * b.x - a.x * b.y;
+	if (n_num % n_den)
+		return 0;
+	const i64 n = n_num / n_den;
+
+	const i64 m_num = p.x - n * a.x;
+	const i64 m_den = b.x;
+	if (m_num % m_den)
+		return 0;
+	const i64 m = m_num / m_den;
+
+	return 3 * n + m;
+}
+
+i64 part1(FILE* fp)
+{
+	i64 result = 0;
+
+	for (;;)
+	{
+		constexpr const char* format =
+			"Button A: X+%" SCNd64 ", Y+%" SCNd64 "\n"
+			"Button B: X+%" SCNd64 ", Y+%" SCNd64 "\n"
+			"Prize: X=%" SCNd64 ", Y=%" SCNd64 "\n";
+
+		vec_t a, b, prize;
+		if (fscanf(fp, format, &a.x, &a.y, &b.x, &b.y, &prize.x, &prize.y) != 6)
+			break;
+
+		result += fewest_tokens(a, b, prize);
+	}
+
+	return result;
+}
+
+i64 part2(FILE* fp)
+{
+	i64 result = 0;
+
+	for (;;)
+	{
+		constexpr const char* format =
+			"Button A: X+%" SCNu64 ", Y+%" SCNu64 "\n"
+			"Button B: X+%" SCNu64 ", Y+%" SCNu64 "\n"
+			"Prize: X=%" SCNu64 ", Y=%" SCNu64 "\n";
+
+		vec_t a, b, prize;
+		if (fscanf(fp, format, &a.x, &a.y, &b.x, &b.y, &prize.x, &prize.y) != 6)
+			break;
+
+		prize.x += 10000000000000;
+		prize.y += 10000000000000;
+		result += fewest_tokens(a, b, prize);
+	}
+
+	return result;
+}
+
+int main(int argc, char** argv)
+{
+	const char* file_path = "/usr/share/aoc2024/day13_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);
+}