package algo.graph;
import ds.graph.Graph;
import java.util.HashSet;
import java.util.Set;
/**
* Created by sherxon on 4/16/17.
*/
/**
* To find if the given graph has cycle , We need to maintain one additional set of exited vertices and do dfs.
* In any step if iteration if a vertex is already in visited set and yet not exited from recusion stack, then
* we can return true. We can optimize using one array with 3 different values.
*
* */
public abstract class CycleDetection {
protected Graph graph;
protected Set<Integer> visited;
protected Set<Integer> exited;
public CycleDetection(Graph graph) {
this.graph = graph;
visited=new HashSet<>();
exited=new HashSet<>();
}
public boolean hasCycle(){
return dfs(1);
}
private boolean dfs(Integer start) {
visited.add(start);
for (Integer neighbor : graph.getNeighbors(start)) {
if(visited.contains(neighbor) && !exited.contains(neighbor)) return true;
if(!visited.contains(neighbor) && dfs(neighbor)) return true;
}
exited.add(start);
return false;
}
}