add solution: clone-graph

Author: dusunax

clone-graph/dusunax.py

@@ -0,0 +1,35 @@
+'''
+# 133. Clone Graph
+This is the problem for copying nodes, which helps you understand the concept of referencing a node & copying the node (creating a new node from the existing one).
+
+👉 Perform recursion DFS with the correct escape condition and handling of NoneType.
+'''
+
+"""
+# Definition for a Node.
+class Node:
+    def __init__(self, val = 0, neighbors = None):
+        self.val = val
+        self.neighbors = neighbors if neighbors is not None else []
+"""
+from typing import Optional
+class Solution:
+    def cloneGraph(self, node: Optional['Node']) -> Optional['Node']:
+        if node is None:
+            return None
+            
+        visited = {}
+        
+        def DFS(currNode):
+            if currNode.val in visited:
+                return visited[currNode.val]
+
+            copiedNode = Node(currNode.val)
+            visited[currNode.val] = copiedNode
+
+            for neighbor in currNode.neighbors:
+                copiedNode.neighbors.append(DFS(neighbor))
+
+            return copiedNode
+
+        return DFS(node)