Method dfs

python/0133-clone-graph.py:5–13

(node)

        oldToNew = {}

        def dfs(node):
            if node in oldToNew:
                return oldToNew[node]

            copy = Node(node.val)
            oldToNew[node] = copy
            for nei in node.neighbors:
                copy.neighbors.append(dfs(nei))
            return copy

        return dfs(node) if node else None