Find the Weak Connected Component in the Directed Graph

Question

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.)

Notice

Sort the element in the set in increasing order

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}

Tags

Union Find

Related Problems

Hard Number of Islands II 16 % Medium Find the Weak Connected Component in the Directed Graph 22 % Medium Find the Connected Component in the Undirected Graph

Analysis

与Find the Connected Component in the Undirected Graph基本相同。

Solution

/**
* Definition for Directed graph.
* class DirectedGraphNode {
*     int label;
*     ArrayList<DirectedGraphNode> neighbors;
*     DirectedGraphNode(int x) { label = x; neighbors = new ArrayList<DirectedGraphNode>(); }
* };
*/

public class Solution {
    class UnionFind{
        HashMap<Integer, Integer> father = new HashMap<Integer, Integer>();
        UnionFind(HashSet<Integer> hashSet){
            for(Integer now : hashSet) {
                father.put(now, now);
            }
        }
        int find(int x){
            int parent =  father.get(x);
            while(parent!=father.get(parent)) {
                parent = father.get(parent);
            }
            return parent;
        }
        int compressed_find(int x){
            int parent =  father.get(x);
            while(parent!=father.get(parent)) {
                parent = father.get(parent);
            }
            int temp = -1;
            int fa = father.get(x);
            while(fa!=father.get(fa)) {
                temp = father.get(fa);
                father.put(fa, parent) ;
                fa = temp;
            }
            return parent;

        }

        void union(int x, int y){
            int fa_x = find(x);
            int fa_y = find(y);
            if(fa_x != fa_y)
            father.put(fa_x, fa_y);
        }
    }
    List<List<Integer> >  print(HashSet<Integer> hashSet, UnionFind uf, int n) {
        List<List <Integer> > ans = new ArrayList<List<Integer>>();
        HashMap<Integer, List <Integer>> hashMap = new HashMap<Integer, List <Integer>>();
        for(int i : hashSet){
            int fa = uf.find(i);
            if(!hashMap.containsKey(fa)) {
                hashMap.put(fa,  new ArrayList<Integer>() );
            }
            List <Integer> now =  hashMap.get(fa);
            now.add(i);
            hashMap.put(fa, now);
        }
        for( List <Integer> now: hashMap.values()) {
            Collections.sort(now);
            ans.add(now);
        }
        return ans;
    }

    public List<List<Integer>> connectedSet2(ArrayList<DirectedGraphNode> nodes){
        // Write your code here

        HashSet<Integer> hashSet = new HashSet<Integer>();
        for(DirectedGraphNode now : nodes){
            hashSet.add(now.label);
            for(DirectedGraphNode neighbour : now.neighbors) {
                hashSet.add(neighbour.label);
            }
        }
        UnionFind uf = new UnionFind(hashSet);


        for(DirectedGraphNode now : nodes){

            for(DirectedGraphNode neighbour : now.neighbors) {
                int fnow = uf.find(now.label);
                int fneighbour = uf.find(neighbour.label);
                if(fnow!=fneighbour) {
                    uf.union(now.label, neighbour.label);
                }
            }
        }


        return print(hashSet , uf, nodes.size());
    }

}