Added algorithm to deeply clone a graph

graphs/deep-clone-graph.py

@@ -0,0 +1,60 @@
+"""
+LeetCode 133. Clone Graph
+https://leetcode.com/problems/clone-graph/
+
+Given a reference of a node in a connected undirected graph.
+
+Return a deep copy (clone) of the graph.
+
+Each node in the graph contains a value (int) and a list (List[Node]) of its
+neighbors.
+"""
+
+
+class Node:
+    def __init__(self, value=0, neighbors=None):
+        self.value = value
+        self.neighbors = neighbors if neighbors is not None else []
+
+
+def clone_graph(node: Node | None) -> None | None:
+    """
+    This function returns a clone of a connected undirected graph.
+    >>> clone_graph(Node(1))
+    Node(1)
+    >>> clone_graph(Node(1, [Node(2)]))
+    Node(1, [Node(2)])
+    >>> clone_graph(None)
+    None
+    """
+    if not node:
+        return None
+
+    originals_to_clones = {}  # map nodes to clones
+
+    def create_clones(node: Node) -> None:
+        if node in originals_to_clones:
+            return
+
+        originals_to_clones[node] = Node(node.value)
+
+        for neighbor in node.neighbors:
+            create_clones(neighbor)
+
+    create_clones(node)
+
+    def connect_clones_to_cloned_neighbors() -> None:
+        for original, clone in originals_to_clones.items():
+            for neighbor in original.neighbors:
+                cloned_neighbor = originals_to_clones[neighbor]
+                clone.neighbors.append(cloned_neighbor)
+
+    connect_clones_to_cloned_neighbors()
+
+    return originals_to_clones[node]
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()