union_and_find_approach_graph

Java/union_and_find_approach_graph

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+
+//Detects cycle in O(n) amortized time complexity.
+
+import java.util.*;
+import java.lang.*;
+import java.io.*;
+
+class Solution
+{
+    //Function to detect cycle in an undirected graph.
+    public boolean isCycle(int V, ArrayList<ArrayList<Integer>> adj)
+    {       
+
+        //Union find
+
+        int[] parent=new int[V];
+
+        Arrays.fill(parent,-1);   
+
+        for(int src=0;src<V;src++){
+
+            for(int des:adj.get(src)){
+
+                if(src<des){
+
+                    int x=find(parent,src);
+                    int y=find(parent,des);
+
+                    if(x==y) return true;
+
+                    union(parent,x,y);
+
+                }
+
+            }
+
+        }
+        return false;
+    }
+
+    private int find(int[] parent,int i){
+
+        if(parent[i]==-1){
+            return i;
+        }
+        int idx=find(parent,parent[i]);
+        parent[i]=idx;
+        return idx;
+    }
+
+    private void union(int[] parent,int x,int y){
+
+        parent[x]=y;
+
+    }
+
+}