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#include <filesystem>
#include <fstream>
#include <iostream>
#include <regex>
#include <set>
#include <tuple>
#include <vector>
using namespace std;
namespace {
struct Point {
long x;
long y;
long vx;
long vy;
};
vector<Point>
read_file(const filesystem::path& filename)
{
ifstream file{ filename };
static const regex pattern{ R"(position=<\s*(-?\d+)\s*,\s*(-?\d+)\s*>\s*velocity=<\s*(-?\d+)\s*,\s*(-?\d+)\s*>)" };
vector<Point> data;
for ( string line; getline(file, line); ) {
smatch match;
if ( regex_match(line, match, pattern) ) {
auto x = stol(match[1]);
auto y = stol(match[2]);
auto vx = stol(match[3]);
auto vy = stol(match[4]);
data.emplace_back(x, y, vx, vy);
}
}
return data;
}
void
get_bounding_box(const vector<Point>& points, long& min_x, long& min_y, long& max_x, long& max_y)
{
min_x = numeric_limits<long>::max();
min_y = numeric_limits<long>::max();
max_x = numeric_limits<long>::min();
max_y = numeric_limits<long>::min();
for ( const auto& point: points ) {
min_x = min(min_x, point.x);
min_y = min(min_y, point.y);
max_x = max(max_x, point.x);
max_y = max(max_y, point.y);
}
}
long
bounding_area(const vector<Point>& points)
{
long min_x = 0;
long min_y = 0;
long max_x = 0;
long max_y = 0;
get_bounding_box(points, min_x, min_y, max_x, max_y);
return 1L * (max_x - min_x + 1) * (max_y - min_y + 1);
}
void
update(vector<Point>& points)
{
for ( auto& point: points ) {
point.x += point.vx;
point.y += point.vy;
}
}
tuple<int, vector<Point>>
get_best(vector<Point> points)
{
auto best_area = numeric_limits<long>::max();
vector<Point> best;
int best_t = 0;
for ( int i = 0; i != 100'000; ++i ) {
update(points);
auto area = bounding_area(points);
if ( area < best_area ) {
best_area = area;
best = points;
best_t = i + 1;
}
}
return { best_t, best };
}
void
print(const vector<Point>& points)
{
set<tuple<long, long>> grid;
for ( const auto [x, y, vx, vy]: points ) {
grid.emplace(x, y);
}
long min_x = 0;
long min_y = 0;
long max_x = 0;
long max_y = 0;
get_bounding_box(points, min_x, min_y, max_x, max_y);
for ( long y = min_y; y <= max_y; ++y ) {
for ( long x = min_x; x <= max_x; ++x ) {
cout << (grid.contains({ x, y }) ? '#' : ' ');
}
cout << '\n';
}
}
void
solve(const vector<Point>& points)
{
auto [time, best_points] = get_best(points);
print(best_points);
cout << "Part 2: " << time << '\n';
}
} // namespace
int
main()
{
auto data = read_file("data/day10.txt");
solve(data);
}
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