forked from Bananymous/banan-os
116 lines
2.3 KiB
C++
116 lines
2.3 KiB
C++
#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);
|
|
}
|