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source/Tree/Centroid.cpp

@@ -0,0 +1,30 @@
+vi adj[N]; bool cent[N];
+int sz[N], par[N];
+
+void getSz(int s){
+    sz[s] = 1;
+    for(auto i:adj[s]){
+        if(cent[i]) continue; if(par[s] == i) continue;
+        par[i] = s; getSz(i); par[i] = 0;
+        sz[s] += sz[i];
+    }
+}
+int getCent(int s, int n){
+    for(auto i:adj[s]) if(!cent[i]&&sz[i]<sz[s]&&sz[i]>n/2)
+        return getCent(i, n);
+    return s;
+}
+
+int cpar[N];
+int getCentTree(int s){
+    getSz(s); int C = getCent(s, sz[s]);    
+    cent[C] = true;
+    for(auto i:adj[C]){
+        if(cent[i]) continue;
+        int c = getCentTree(i);
+        cpar[c] = C;
+    }
+    return C;
+}
+
+int C = getCentTree(1); cpar[C] = -1;