Find the Weak Connected Component in the Directed Graph

Description:

Find the number Weak Connected Component in the directed graph. Each node in the graph contains a label and a list of its neighbors. (a connected set of a directed graph is a subgraph in which any two vertices are connected by direct edge path.)

Example

Given graph:

A----->B  C
 \     |  | 
  \    |  |
   \   |  |
    \  v  v
     ->D  E <- F

Return {A,B,D}, {C,E,F}. Since there are two connected component which are {A,B,D} and {C,E,F}

Solution:

( Union-Find Sets )

/**
 * Definition for Directed graph.
 * struct DirectedGraphNode {
 *     int label;
 *     vector<DirectedGraphNode *> neighbors;
 *     DirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
private:
	unordered_map<DirectedGraphNode*, DirectedGraphNode*> cache;
	DirectedGraphNode* find(DirectedGraphNode* node) {
		if (cache[node] != node)
			cache[node] = find(cache[node]);
		return cache[node];
	}

	void merge(DirectedGraphNode* n1, DirectedGraphNode* n2) {
		auto f1 = find(n1);
		auto f2 = find(n2);
		if (f1 != f2) cache[f2] = f1;
	}

public:
	/**
	 * @param nodes a array of directed graph node
	 * @return a connected set of a directed graph
	*/
	vector<vector<int>> connectedSet2(vector<DirectedGraphNode*>& nodes) {
		vector<vector<int>> rc;
		for (auto& node : nodes) cache[node] = node;
		for (auto& node : nodes) 
			for (auto& ngb : node->neighbors)
				merge(node, ngb);
		unordered_map<DirectedGraphNode*, int> index;
		for (auto& node : nodes) {
			auto father = find(node);
			if (index.find(father) == index.end()) {
				rc.push_back(vector<int>({node->label}));
				index[father] = rc.size()-1;
			} else rc[index[father]].push_back(node->label);
		}

		return rc;
	}
};