Find the Weak Connected Component in the Directed Graph

Description:

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

Solution:

/**
* 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;
}
};