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#include <algorithm>
#include <array>
#include <cmath>
#include <iostream>
#include <map>
using namespace std;
namespace {
void
part1(int value)
{
auto ring = static_cast<int>(ceil((sqrt(value) - 1) / 2));
auto side_len = (2 * ring) + 1;
auto max_value = side_len * side_len;
array<int, 4> centers = {
max_value - ring - (2 * ring * 0),
max_value - ring - (2 * ring * 1),
max_value - ring - (2 * ring * 2),
max_value - ring - (2 * ring * 3)
};
auto* itr = ranges::min_element(centers, {}, [value](int rhs) { return abs(value - rhs); });
auto dist_to_center = abs(value - *itr);
cout << "Part1: " << ring + dist_to_center << '\n';
}
void
part2(int value)
{
static const array<tuple<int, int>, 4> dirs{
make_tuple(1, 0), // right
make_tuple(0, -1), // up
make_tuple(-1, 0), // left
make_tuple(0, 1), // down
};
static const array<int, 3> offsets = { -1, 0, 1 };
map<tuple<int, int>, int> grid; // (x,y) => value
int x = 0;
int y = 0;
int steps = 1;
grid[{ x, y }] = 1;
while ( true ) {
for ( const auto [dx, dy]: dirs ) {
for ( int _ = 0; _ != steps; ++_ ) {
x += dx;
y += dy;
int sum = 0;
for ( const auto off_x: offsets ) {
for ( const auto off_y: offsets ) {
if ( off_x == 0 && off_y == 0 ) {
continue;
}
const auto pos = make_tuple(x + off_x, y + off_y);
if ( grid.contains(pos) ) {
sum += grid.at(pos);
}
}
}
if ( sum > value ) {
cout << "Part2: " << sum << '\n';
return;
}
grid[{ x, y }] = sum;
}
if ( dx == 0 ) {
++steps;
}
}
}
}
} // namespace
int
main()
{
static const auto puzzle = 265149;
part1(puzzle);
part2(puzzle);
}
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