banan-os/userspace/aoc2023/day24/main.cpp

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2023-12-26 14:10:49 +02:00
#include <BAN/Vector.h>
#include <ctype.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;
struct Hailstone
{
double px, py, pz;
double vx, vy, vz;
};
i64 parse_i64(BAN::StringView str)
{
while (isspace(str.front()))
str = str.substring(1);
bool negative = str.front() == '-';
if (negative)
str = str.substring(1);
i64 result = 0;
for (char c : str)
if (isdigit(c))
result = (result * 10) + (c - '0');
return negative ? -result : result;
}
BAN::Vector<Hailstone> parse_hailstones(FILE* fp)
{
BAN::Vector<Hailstone> hailstones;
char buffer[128];
while (fgets(buffer, sizeof(buffer), fp))
{
BAN::StringView line(buffer);
ASSERT(line.back() == '\n');
line = line.substring(0, line.size() - 1);
if (line.empty())
break;
auto position_velocity_strs = MUST(line.split('@'));
ASSERT(position_velocity_strs.size() == 2);
Hailstone hailstone;
auto position_strs = MUST(position_velocity_strs[0].split(','));
ASSERT(position_strs.size() == 3);
hailstone.px = parse_i64(position_strs[0]);
hailstone.py = parse_i64(position_strs[1]);
hailstone.pz = parse_i64(position_strs[2]);
auto velocity_strs = MUST(position_velocity_strs[1].split(','));
ASSERT(velocity_strs.size() == 3);
hailstone.vx = parse_i64(velocity_strs[0]);
hailstone.vy = parse_i64(velocity_strs[1]);
hailstone.vz = parse_i64(velocity_strs[2]);
MUST(hailstones.push_back(hailstone));
}
return hailstones;
}
i64 puzzle1(FILE* fp)
{
auto hailstones = parse_hailstones(fp);
i64 result = 0;
for (size_t i = 0; i < hailstones.size(); i++)
{
for (size_t j = i + 1; j < hailstones.size(); j++)
{
const auto& h1 = hailstones[i];
const auto& h2 = hailstones[j];
// skip parallel lines
if (h1.vy * h2.vx == h2.vy * h1.vx)
continue;
const double t2 = ((h2.py - h1.py) * h1.vx - (h2.px - h1.px) * h1.vy) / (h2.vx * h1.vy - h1.vx * h2.vy);
if (t2 < 0.0)
continue;
const double t1 = ((h2.py - h1.py) + t2 * h2.vy) / h1.vy;
if (t1 < 0.0)
continue;
const double x = h2.px + t2 * h2.vx;
const double y = h2.py + t2 * h2.vy;
constexpr double min = 200000000000000.0;
constexpr double max = 400000000000000.0;
if ((min <= x && x <= max) && (min <= y && y <= max))
result++;
}
}
return result;
}
i64 puzzle2(FILE* fp)
{
(void)fp;
return -1;
}
int main(int argc, char** argv)
{
const char* file_path = "/usr/share/aoc2023/day24_input.txt";
if (argc >= 2)
file_path = argv[1];
FILE* fp = fopen(file_path, "r");
if (fp == nullptr)
{
perror("fopen");
return 1;
}
printf("puzzle1: %" PRId64 "\n", puzzle1(fp));
fseek(fp, 0, SEEK_SET);
printf("puzzle2: %" PRId64 "\n", puzzle2(fp));
fclose(fp);
}