namespace lca { int d[MN], L[MN][20]; void dfs(vector * G, int u = 1, int p = 0) { d[u] = d[p] + 1, L[u][0] = p; for (int i = 0; i < 18 && L[u][i]; i++) L[u][i + 1] = L[L[u][i]][i]; for (auto& v : G[u]) if (v != p) dfs(G, v, u); } int lca(vector * G, int u, int v) { if (d[u] > d[v]) swap(u, v); for (int i = 18; i >= 0; --i) if (d[v] - (1 << i) >= d[u]) v = L[v][i]; if (u == v) return u; for (int i = 18; i >= 0; --i) if (L[u][i] && L[u][i] != L[v][i]) u = L[u][i], v = L[v][i]; return L[u][0]; } inline int dist(vector * G, int u, int v) { return d[u]+d[v]-2*d[lca(G, u, v)]; } }