clone a graph

Author: ZapDos7

README.md

@@ -135,7 +135,7 @@
 - [x] [Terminology and Representations of Graphs](http://www.techiedelight.com/terminology-and-representations-of-graphs/)
 - [x] Given a list of edges and tasked to build your own graph from the edges
 - [x] Implement Dijkstra’s algorithm (implemented Weighted Graph to showcase this)
-
+- [x] [Clone graph](https://leetcode.com/problems/clone-graph/)
 ### Matrix
 
 ### Trees
@@ -275,7 +275,6 @@
     - [ ] Implement Floyd-Warshall algorithm
     - [ ] Implement Prim’s algorithm
     - [ ] Implement Kruskal’s algorithm
-    - [ ] [Clone graph](https://leetcode.com/problems/clone-graph/)
     - [ ] [Course Schedule](https://leetcode.com/problems/course-schedule/)
     - [ ] [Alien Dictionary](https://leetcode.com/problems/alien-dictionary/)
     - [ ] [Pacific Atlantic Water Flow](https://leetcode.com/problems/pacific-atlantic-water-flow/)

src/dataStructures/graphs/Node.java

@@ -0,0 +1,35 @@
+package dataStructures.graphs;
+
+import java.util.ArrayList;
+import java.util.List;
+
+// LeetCode Node for examples
+public class Node {
+    public int val;
+    public List<Node> neighbors;
+
+    public Node() {
+        val = 0;
+        neighbors = new ArrayList<>();
+    }
+
+    public Node(int _val) {
+        val = _val;
+        neighbors = new ArrayList<>();
+    }
+
+    public Node(int _val, ArrayList<Node> _neighbors) {
+        val = _val;
+        neighbors = _neighbors;
+    }
+
+    // My addition: toString()
+
+    @Override
+    public String toString() {
+        return "Node{" +
+                "val=" + val +
+                ", neighbors=" + neighbors +
+                '}';
+    }
+}

src/dataStructures/graphs/cloner/GraphCloner.java

@@ -0,0 +1,42 @@
+package dataStructures.graphs.cloner;
+
+import dataStructures.graphs.Node;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class GraphCloner {
+
+    public static void main(String[] args) {
+        Node n1 = new Node(1);
+        Node n2 = new Node(2);
+        n2.neighbors = List.of(n1);
+        Node root = new Node(0);
+        root.neighbors = List.of(n1, n2);
+        System.out.println("OG:    " + root);
+        System.out.println("Clone: " + cloneGraph(root));
+    }
+
+    // DFS
+    public static Node cloneGraph(Node node) {
+        Map<Node, Node> map = new HashMap<>();
+
+        if (node == null) return null;
+
+        if (map.containsKey(node)) {
+            return map.get(node); // already cloned, use the previously cloned one
+        }
+
+        // Clone the node before recursion
+        Node clone = new Node(node.val); // create new node with same value
+        map.put(node, clone);
+
+        // Clone all the neighbors recursively
+        for (Node neighbor : node.neighbors) {
+            clone.neighbors.add(cloneGraph(neighbor));
+        }
+
+        return clone;
+    }
+}