Graph/lca.cpp


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struct lca {
    int d[MN], L[MN][20];
    void dfs(vector<int> * 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<int> * 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];
    }
}