[LintCode] Find the Weak Connected Component in the Directed Graph

Find the Weak Connected Component in the Directed Graph

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}

Note

Sort the element in the set in increasing order

 

Union-Find，并查集！注意fa每次都要重新求，因为fa的值可能在之前的循环中被更新。

/**
 * Definition for Directed graph.
 * struct DirectedGraphNode {
 *     int label;
 *     vector<DirectedGraphNode *> neighbors;
 *     DirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    /**
     * @param nodes a array of directed graph node
     * @return a connected set of a directed graph
     */
    int find(unordered_map<int, int> &father, int x) {
        if (father.find(x) == father.end()) {
            father[x] = x;
            return x;
        }
        while (x != father[x]) x = father[x];
        return x;
    }
    vector<vector<int>> connectedSet2(vector<DirectedGraphNode*>& nodes) {
        // Write your code here
        unordered_map<int, int> father;
        int fa, fb, fn;
        for (auto &n : nodes) {
            for (auto &nn : n->neighbors) {
                fa = find(father, n->label);
                fb = find(father, nn->label);
                if (fa != fb) {
                    if (fa > fb) father[fa] = fb;
                    else father[fb] = fa;
                }
            }
        }
        unordered_map<int, vector<int>> comp;
        for (auto &n : nodes) {
            fn = find(father, n->label);
            comp[fn].push_back(n->label);
        }
        vector<vector<int>> res;
        for (auto &c : comp) {
            sort(c.second.begin(), c.second.end());
            res.push_back(c.second);
        }
        return res;
    }
};