Method build

code/graph/hld.cpp:31–32

      if (adj[u][i] != parent[u] && adj[u][i] != best)
        part(curhead = adj[u][i]); }
  void build(int r = 0) {
    curloc = 0, csz(curhead = r), part(r); }
  int lca(int u, int v) {
    vi uat, vat; int res = -1;
    while (u != -1) uat.push_back(u), u = parent[head[u]];