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namespace centroid {
int sz[MX], cpar[MX];
bitset<MX> vis;
void dfs(vector<int> * G, int u, int p = 0) {
sz[u] = 1;
for (int v : G[u]) if (v != p && !vis[v]) dfs(G, v, u), sz[u] += sz[v];
}
int centroid(vector<int> * G, int u) {
dfs(G, u);
int num = sz[u], p = 0;
do {
int nxt = 0;
for (int v : G[u]) if (v != p && !vis[v] && 2*sz[v] > num) nxt = v;
p = u, u = nxt;
} while (u);
return p;
}
void centroid_decomp(vector<int> * G, int u = 1, int p = 0) {
int c = centroid(G, u);
vis[c] = 1, cpar[c] = p;
for (int v : G[c]) if (!vis[v]) centroid_decomp(G, v, c);
}
}
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