/*

* Sample usage: java Cycle tinyG.txt

* Sample usage: java Cycle mediumG.txt

*/

public class Cycle {

private boolean[] marked;

private boolean hasCycle;

// We assume there is no self-loop or parallel edges

public Cycle(Graph G){

marked = new boolean[G.V()];

for (int s=0; s<G.V(); s++)

if (!marked[s])

dfs(G, s, s); // The second s is a dummy variable, which can be set to -1

}

private void dfs(Graph G, int v, int u){

marked[v] = true;

for (int w : G.adj(v))

if (!marked[w])

dfs(G, w, v);

else if (w!=u) hasCycle=true;

}

public boolean marked(int w){

return marked[w];

}

public boolean hasCycle(){

return hasCycle;

}

public static void main(String[] args) {

In in = new In(args[0]);

Graph G = new Graph(in);

Cycle finder = new Cycle(G);

if (finder.hasCycle()) {

StdOut.println("Graph is cyclic");

}

else {

StdOut.println("Graph is acyclic");

}

}

}