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

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);
hashMap.put(fa, now);
}
for( List <Integer> now: hashMap.values()) {
Collections.sort(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){
for(DirectedGraphNode neighbour : now.neighbors) {
}
}
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());
}

}