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#include "aoc.h"
#include <deque>
#include <set>
namespace aoc2016 {
struct pos {
int64_t x;
int64_t y;
int64_t n;
friend bool operator<(pos p1, pos p2) { return p1.x < p2.x ? true : p1.x > p2.x ? false : p1.y < p2.y; }
bool operator==(pos p) const noexcept { return x == p.x && y == p.y; }
};
bool is_space(int64_t x, int64_t y, int64_t favorite) {
int64_t a = x * x + 3 * x + 2 * x * y + y + y * y + favorite;
int64_t c = __builtin_popcount(a);
return x >= 0 && y >= 0 && (c & 1) == 0;
}
int64_t bfs(pos start, pos end, int64_t favorite, std::set<pos>& visited) {
std::deque<pos> q;
q.push_back(start);
visited.insert(start);
while (!q.empty()) {
auto s = q.size();
while (s-- > 0) {
auto p0 = q.front();
q.pop_front();
visited.insert(p0);
if (p0 == end) {
return p0.n;
} else {
pos ns[4] = {
{p0.x - 1, p0.y, p0.n + 1},
{p0.x + 1, p0.y, p0.n + 1},
{p0.x, p0.y - 1, p0.n + 1},
{p0.x, p0.y + 1, p0.n + 1},
};
for (pos p : ns) {
if (is_space(p.x, p.y, favorite)) {
auto it = visited.find(p);
if (it == visited.end() || it->n > p.n) {
q.push_back(p);
}
}
}
}
}
}
return INT64_MAX;
}
std::pair<int64_t, int64_t> day13(line_view) {
std::set<pos> visited;
int64_t s = bfs({1, 1, 0}, {31, 39, INT64_MAX}, 1352, visited);
int64_t total{0};
for (auto& p : visited) {
if (p.n <= 50) {
total += 1;
}
}
return {s, total};
}
} // namespace aoc2016
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