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> connectedSet2(vector<DirectedGraphNode>& nodes) {
vector<vector> 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({node->label}));
index[father] = rc.size()-1;
} else rc[index[father]].push_back(node->label);
}

return rc;
}
};