int64_t countPairs(HashSet &hs, int mask) {
hs.reset();
int64_t ans = 0;
for (int i = 0; i < N; i++) {
int m = mask;
pair<int, int> key = make_pair(0, 0);
while (m) {
int x = __builtin_ctz(m);
hashf(key, W[i][x]);
m -= (1<<x);
}
if (hs.contains(key)) ans += hs[key]++;
else hs.insert(key);
}
return ans;
}
