dsu on trees in c++

Disjoint Set Union (DSU)/dsu_on_trees.cpp

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+// CPP code to find maximum subtree such 
+// that all nodes are even in weight 
+#include<bits/stdc++.h> 
+
+using namespace std; 
+
+#define N 100010 
+
+// Structure for Edge 
+struct Edge 
+{ 
+	int u, v; 
+}; 
+
+/* 
+	'id': stores parent of a node. 
+	'sz': stores size of a DSU tree. 
+*/
+int id[N], sz[N]; 
+
+// Function to assign root 
+int Root(int idx) 
+{ 
+	int i = idx; 
+
+	while(i != id[i]) 
+		id[i] = id[id[i]], i = id[i]; 
+
+	return i; 
+} 
+
+// Function to find Union 
+void Union(int a, int b) 
+{ 
+	int i = Root(a), j = Root(b); 
+
+	if (i != j) 
+	{ 
+		if(sz[i] >= sz[j]) 
+		{ 
+			id[j] = i, sz[i] += sz[j]; 
+			sz[j] = 0; 
+		} 
+		else
+		{ 
+			id[i] = j, sz[j] += sz[i]; 
+			sz[i] = 0; 
+		} 
+	} 
+} 
+
+// Utility function for Union 
+void UnionUtil(struct Edge e[], int W[], int q) 
+{ 
+
+	for(int i = 0; i < q; i++) 
+	{ 
+		// Edge between 'u' and 'v' 
+		int u, v; 
+		u = e[i].u, v = e[i].v; 
+
+		// 0-indexed nodes 
+		u--, v--; 
+
+		// If weights of both 'u' and 'v' 
+		// are even then we make union of them. 
+		if(W[u] % 2 == 0 && W[v] % 2 == 0) 
+					Union(u,v); 
+	} 
+} 
+
+// Function to find maximum 
+// size of DSU tree 
+int findMax(int n, int W[]) 
+{ 
+	int maxi = 0; 
+	for(int i = 1; i <= n; i++) 
+		if(W[i] % 2 == 0) 
+			maxi = max(maxi, sz[i]); 
+
+	return maxi; 
+} 
+
+// Driver code 
+int main() 
+{ 
+	/* 
+		Nodes are 0-indexed in this code 
+		So we have to make necessary changes 
+		while taking inputs 
+	*/
+
+	// Weights of nodes 
+	int W[] = {1, 2, 6, 4, 2, 0, 3}; 
+
+	// Number of nodes in a tree 
+	int n = sizeof(W) / sizeof(W[0]); 
+
+	// Initializing every node as 
+	// a tree with single node. 
+	for(int i = 0; i < n; i++) 
+			id[i] = i, sz[i] = 1; 
+
+	Edge e[] = {{1, 2}, {1, 3}, {2, 4}, 
+				{2, 5}, {4, 6}, {6, 7}}; 
+
+	int q = sizeof(e) / sizeof(e[0]); 
+
+	UnionUtil(e, W, q); 
+
+	// Find maximum size of DSU tree. 
+	int maxi = findMax(n, W); 
+
+	printf("Maximum size of the subtree with "); 
+	printf("even weighted nodes = %d\n", maxi); 
+
+	return 0; 
+}