Add CloneGraph class to clone a graph

Implement a method to create a deep copy of a graph using BFS.

Author: harshithasudhakar

Graphs/Problems/CloneGraph.java

@@ -0,0 +1,57 @@
+/*
+// 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 CloneGraph { //create a deep copy of the given graph
+    public Node cloneGraph(Node node) {
+        Queue<Node> q = new LinkedList<>();
+
+        if(node == null){
+            return node;
+        }
+
+        q.add(node);
+
+        Map<Node, Node> map = new HashMap<>();
+        Node current;
+
+        Node newNode = new Node();
+        newNode.val = node.val;
+        map.put(node, newNode);
+        
+        while(!q.isEmpty()){
+            current = q.poll();
+            Node currentClone = map.get(current);
+
+            for(Node neighboringNode : current.neighbors){
+                if(map.containsKey(neighboringNode)){
+                    currentClone.neighbors.add(map.get(neighboringNode));
+                }
+                else{
+                    Node newCloneNeighbor = new Node(neighboringNode.val);
+                    map.put(neighboringNode, newCloneNeighbor);
+                    q.add(neighboringNode);
+                    currentClone.neighbors.add(newCloneNeighbor);
+                }
+            }
+        }
+
+        return map.get(node);
+    }
+}