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#include <bit>
#include <iostream>
#include <queue>
#include <set>
using namespace std;
namespace {
using pos_type = tuple<long, long>;
bool
is_wall(long x, long y, long number)
{
auto result = (x * x) + (3 * x) + (2 * x * y) + y + (y * y);
result += number;
auto num = popcount(static_cast<unsigned long>(result));
return (num % 2) != 0;
}
int
part1(long initial_value, pos_type dest)
{
pos_type start_pos = { 1, 1 };
set<pos_type> seen;
queue<tuple<pos_type, int>> queue; // pos, #steps
seen.emplace(start_pos);
queue.emplace(start_pos, 0);
while ( !queue.empty() ) {
auto [pos, steps] = queue.front();
queue.pop();
if ( pos == dest ) {
return steps;
}
static const pos_type dirs[] = { { -1, 0 }, { 0, -1 }, { 1, 0 }, { 0, 1 } };
for ( const auto [dx, dy]: dirs ) {
auto [x, y] = pos;
x += dx;
y += dy;
if ( x < 0 || y < 0 ) {
continue;
}
if ( seen.contains({ x, y }) ) {
continue;
}
if ( !is_wall(x, y, initial_value) ) {
seen.emplace(x, y);
queue.emplace(pos_type{ x, y }, steps + 1);
}
}
}
return -1; // Error
}
int
part2(long initial_value, int max_steps)
{
pos_type start_pos = { 1, 1 };
int count = 0;
set<pos_type> seen;
queue<tuple<pos_type, int>> queue; // pos, #steps
seen.emplace(start_pos);
queue.emplace(start_pos, 0);
while ( !queue.empty() ) {
auto [pos, steps] = queue.front();
queue.pop();
if ( steps > max_steps ) {
continue;
}
++count;
static const pos_type dirs[] = { { -1, 0 }, { 0, -1 }, { 1, 0 }, { 0, 1 } };
for ( const auto [dx, dy]: dirs ) {
auto [x, y] = pos;
x += dx;
y += dy;
if ( x < 0 || y < 0 ) {
continue;
}
if ( seen.contains({ x, y }) ) {
continue;
}
if ( !is_wall(x, y, initial_value) ) {
seen.emplace(x, y);
queue.emplace(pos_type{ x, y }, steps + 1);
}
}
}
return count;
}
} // namespace
int
main()
{
#if 0
static const long number = 10;
static const pos_type dest = { 7, 4 };
#else
static const long number = 1352;
static const pos_type dest = { 31, 39 };
#endif
cout << part1(number, dest) << '\n';
cout << part2(number, 50) << '\n';
}
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