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#include <filesystem>
#include <fstream>
#include <iostream>
#include <tuple>
#include <vector>
using namespace std;
namespace {
using Pos = tuple<long, long>; // (x, y)
using Segment = tuple<Pos, Pos>; // (p1, p2)
vector<Pos>
read_file(const filesystem::path& filename)
{
ifstream file{ filename };
vector<Pos> data;
long x{};
long y{};
char skip{};
while ( file >> x >> skip >> y ) {
data.emplace_back(x, y);
}
return data;
}
void
part1(const vector<Pos>& data)
{
auto area = numeric_limits<long>::min();
for ( size_t i = 0; i != data.size(); ++i ) {
for ( size_t j = i + 1; j != data.size(); ++j ) {
const auto [x1, y1] = data[i];
const auto [x2, y2] = data[j];
const auto width = abs(x1 - x2) + 1;
const auto height = abs(y1 - y2) + 1;
area = max(area, width * height);
}
}
cout << "Part 1: " << area << '\n';
}
vector<Segment>
build_edges(const vector<Pos>& data)
{
vector<Segment> edges;
for ( size_t i = 0; i != data.size(); ++i ) {
edges.emplace_back(data[i], data[(i + 1) % data.size()]);
}
return edges;
}
bool
intersects(const Segment& line, const tuple<long, long, long, long>& rect)
{
const auto [start, end] = line;
const auto [x1, y1] = start;
const auto [x2, y2] = end;
const auto [left, top, right, bottom] = rect;
if ( x1 == x2 ) {
if ( x1 <= left || x1 >= right ) {
return false;
}
const auto min_y = min(y1, y2);
const auto max_y = max(y1, y2);
return max_y > top && min_y < bottom;
}
if ( y1 == y2 ) {
if ( y1 <= top || y1 >= bottom ) {
return false;
}
auto min_x = min(x1, x2);
auto max_x = max(x1, x2);
return max_x > left && min_x < right;
}
return false;
}
bool
contains(const vector<Segment>& poly, const tuple<long, long, long, long>& rect)
{
return ranges::all_of(poly, [&](const auto& line) { return !intersects(line, rect); });
}
void
part2(const vector<Pos>& data)
{
const auto poly = build_edges(data);
auto max_area = numeric_limits<long>::min();
for ( size_t i = 0; i != data.size(); ++i ) {
for ( size_t j = i + 1; j != data.size(); ++j ) {
const auto [x1, y1] = data[i];
const auto [x2, y2] = data[j];
const auto width = abs(x1 - x2) + 1;
const auto height = abs(y1 - y2) + 1;
const auto area = width * height;
if ( area <= max_area ) {
continue;
}
const auto left = min(x1, x2);
const auto right = max(x1, x2);
const auto top = min(y1, y2);
const auto bottom = max(y1, y2);
if ( contains(poly, { left, top, right, bottom }) ) {
max_area = area;
}
}
}
cout << "Part 2: " << max_area << '\n';
}
} // namespace
int
main()
{
auto data = read_file("data/day09.txt");
part1(data);
part2(data);
}
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