Create Detect cycle in an undirected graph (using DFS).java

Author: krushnadurole

Data_Structures/Detect cycle in an undirected graph (using DFS).java

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+import java.util.*;
+
+class Solution {
+    private boolean dfs(int node, int parent, int vis[], ArrayList<ArrayList<Integer>> 
+    adj) {
+        vis[node] = 1; 
+        // go to all adjacent nodes
+        for(int adjacentNode: adj.get(node)) {
+            if(vis[adjacentNode]==0) {
+                if(dfs(adjacentNode, node, vis, adj) == true) 
+                    return true; 
+            }
+            // if adjacent node is visited and is not its own parent node
+            else if(adjacentNode != parent) return true; 
+        }
+        return false; 
+    }
+    // Function to detect cycle in an undirected graph.
+    public boolean isCycle(int V, ArrayList<ArrayList<Integer>> adj) {
+       int vis[] = new int[V]; 
+       for(int i = 0;i<V;i++) {
+           if(vis[i] == 0) {
+               if(dfs(i, -1, vis, adj) == true) return true; 
+           }
+       }
+       return false; 
+    }
+    public static void main(String[] args)
+    {
+        ArrayList<ArrayList<Integer>> adj = new ArrayList<>();
+        for (int i = 0; i < 4; i++) {
+            adj.add(new ArrayList < > ());
+        }
+        adj.get(1).add(2);
+        adj.get(2).add(1);
+        adj.get(2).add(3);
+        adj.get(3).add(2);
+                
+        Solution obj = new Solution();
+        boolean ans = obj.isCycle(4, adj);
+        if (ans)
+            System.out.println("1");    
+        else
+            System.out.println("0");
+    }
+
+}