140 lines
2.8 KiB
C++
140 lines
2.8 KiB
C++
#include <BAN/StringView.h>
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#include <BAN/Vector.h>
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#include <ctype.h>
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#include <inttypes.h>
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#include <stdio.h>
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using i8 = int8_t;
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using i16 = int16_t;
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using i32 = int32_t;
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using i64 = int64_t;
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using u8 = uint8_t;
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using u16 = uint16_t;
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using u32 = uint32_t;
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using u64 = uint64_t;
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struct Hailstone
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{
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double px, py, pz;
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double vx, vy, vz;
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};
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i64 parse_i64(BAN::StringView str)
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{
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while (isspace(str.front()))
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str = str.substring(1);
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bool negative = str.front() == '-';
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if (negative)
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str = str.substring(1);
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i64 result = 0;
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for (char c : str)
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if (isdigit(c))
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result = (result * 10) + (c - '0');
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return negative ? -result : result;
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}
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BAN::Vector<Hailstone> parse_hailstones(FILE* fp)
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{
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BAN::Vector<Hailstone> hailstones;
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char buffer[128];
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while (fgets(buffer, sizeof(buffer), fp))
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{
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BAN::StringView line(buffer);
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ASSERT(line.back() == '\n');
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line = line.substring(0, line.size() - 1);
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if (line.empty())
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break;
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auto position_velocity_strs = MUST(line.split('@'));
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ASSERT(position_velocity_strs.size() == 2);
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Hailstone hailstone;
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auto position_strs = MUST(position_velocity_strs[0].split(','));
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ASSERT(position_strs.size() == 3);
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hailstone.px = parse_i64(position_strs[0]);
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hailstone.py = parse_i64(position_strs[1]);
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hailstone.pz = parse_i64(position_strs[2]);
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auto velocity_strs = MUST(position_velocity_strs[1].split(','));
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ASSERT(velocity_strs.size() == 3);
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hailstone.vx = parse_i64(velocity_strs[0]);
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hailstone.vy = parse_i64(velocity_strs[1]);
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hailstone.vz = parse_i64(velocity_strs[2]);
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MUST(hailstones.push_back(hailstone));
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}
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return hailstones;
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}
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i64 puzzle1(FILE* fp)
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{
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auto hailstones = parse_hailstones(fp);
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i64 result = 0;
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for (size_t i = 0; i < hailstones.size(); i++)
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{
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for (size_t j = i + 1; j < hailstones.size(); j++)
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{
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const auto& h1 = hailstones[i];
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const auto& h2 = hailstones[j];
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// skip parallel lines
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if (h1.vy * h2.vx == h2.vy * h1.vx)
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continue;
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const double t2 = ((h2.py - h1.py) * h1.vx - (h2.px - h1.px) * h1.vy) / (h2.vx * h1.vy - h1.vx * h2.vy);
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if (t2 < 0.0)
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continue;
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const double t1 = ((h2.py - h1.py) + t2 * h2.vy) / h1.vy;
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if (t1 < 0.0)
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continue;
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const double x = h2.px + t2 * h2.vx;
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const double y = h2.py + t2 * h2.vy;
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constexpr double min = 200000000000000.0;
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constexpr double max = 400000000000000.0;
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if ((min <= x && x <= max) && (min <= y && y <= max))
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result++;
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}
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}
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return result;
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}
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i64 puzzle2(FILE* fp)
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{
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(void)fp;
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return -1;
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}
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int main(int argc, char** argv)
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{
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const char* file_path = "/usr/share/aoc2023/day24_input.txt";
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if (argc >= 2)
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file_path = argv[1];
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FILE* fp = fopen(file_path, "r");
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if (fp == nullptr)
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{
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perror("fopen");
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return 1;
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}
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printf("puzzle1: %" PRId64 "\n", puzzle1(fp));
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fseek(fp, 0, SEEK_SET);
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printf("puzzle2: %" PRId64 "\n", puzzle2(fp));
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fclose(fp);
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}
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