USACO Open 2019 Platinum - Valleys

No need to measure "curvature" ... Just maintain # of holes in each region with two DSUs.

int N, h[750][750];

int hsh(pi a) {
    return N*a.f+a.s;
}

bool valid(pi a) {
    return 0 <= a.f && a.f < N && 0 <= a.s && a.s < N;
}