package algo.graph;
/**
* Created by sherxon on 2017-04-09.
*/
import algo.UnionFind;
import ds.graph.Edge;
import ds.graph.WeightedGraph;
import java.util.ArrayList;
import java.util.List;
import java.util.PriorityQueue;
/**
* This is another greedy algorithm to find Minimum Spanning Tree of a connected weighted Graph.
* The idea is choosing least weighted edge until all vertex are in the same connected component. In the beginning
* all vertices are considered as separate components and connect them by choosing least weighted edge.
* Union Find algorithm is used to keep track of connected components. Running time is O(E logE)
* */
public class KruskalsMST {
private WeightedGraph graph;
private UnionFind unionFind;
public KruskalsMST(WeightedGraph graph) {
this.graph = graph;
this.unionFind=new UnionFind(graph.size());
}
public List<Edge> getMST() {
List<Edge> list = new ArrayList<>();
PriorityQueue<Edge> q = new PriorityQueue<>(graph.getEdges());
while (!q.isEmpty()){
Edge minEdge=q.remove(); // remove min Edge and check if both vertices of this edge is connected
if(!unionFind.connected(minEdge.getFrom(), minEdge.getTo())){
list.add(minEdge);
unionFind.union(minEdge.getFrom(), minEdge.getTo()); // make both vertices one component
}
}
return list;
}
}