Create Clone_Graph.java

Author: 17tanya

Clone_Graph.java

@@ -0,0 +1,52 @@
+// Leetcode 133. Clone Graph
+// Question - https://leetcode.com/problems/clone-graph/
+
+/*
+// Definition for a Node.
+class Node {
+    public int val;
+    public List<Node> neighbors;
+    
+    public Node() {
+        val = 0;
+        neighbors = new ArrayList<Node>();
+    }
+    
+    public Node(int _val) {
+        val = _val;
+        neighbors = new ArrayList<Node>();
+    }
+    
+    public Node(int _val, ArrayList<Node> _neighbors) {
+        val = _val;
+        neighbors = _neighbors;
+    }
+}
+*/
+class Solution {
+    
+    //to keep track of already explored nodes 
+    HashMap<Integer,Node> map = new HashMap<Integer,Node>();
+    
+    public Node cloneGraph(Node node) {
+        if(node==null) return null; //empty graph
+        
+        //if the node is already explored then return the newly created node which is stored in the map
+        if(map.containsKey(node.val)) return map.get(node.val);
+        
+        //creating new node from the old node
+        Node curr = new Node(node.val, new ArrayList<>());
+        
+        //adding value to the map
+        //NOTE - the neighbours have not been added yet. This is because if we don't do this step here our code might get stuck in an infite recursion - this will heppen when there is a cycle.
+        //example - Node 5 is neighbour of Node 6. Node 5 will call clone(Node 6) and Node(Clone 6) will call clone(Node 5) and so on...
+        //to avoid this as soon as we create a new node of Node 5, we put it's object in our map. When Node 5 call clone(Node 6) and then Node 6 calls clone(Node 5) an object from the map is returned. Preventing code failure.
+        map.put(node.val,curr);
+        
+        for(Node neighbor : node.neighbors){
+            curr.neighbors.add(cloneGraph(neighbor));
+        }
+        
+        return curr;
+    }
+}