"""
133. Clone Graph
Difficulty: Medium
https://leetcode.com/problems/clone-graph/

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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 {
    public int val;
    public List<Node> neighbors;
}



Test case format:

For simplicity, each node's value is the same as the node's index
(1-indexed). For example, the first node with val == 1, the second
node with val == 2, and so on. The graph is represented in the test
case using an adjacency list.

An adjacency list is a collection of unordered lists used to
represent a finite graph. Each list describes the set of neighbors of
a node in the graph.

The given node will always be the first node with val = 1. You must
return the copy of the given node as a reference to the cloned graph.



Example 1:

Input: adjList = [[2,4],[1,3],[2,4],[1,3]]
Output: [[2,4],[1,3],[2,4],[1,3]]
Explanation: There are 4 nodes in the graph.
1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node
(val = 4).
2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node
(val = 3).
3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node
(val = 4).
4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node
(val = 3).

Example 2:

Input: adjList = [[]]
Output: [[]]
Explanation: Note that the input contains one empty list. The graph
consists of only one node with val = 1 and it does not have any
neighbors.

Example 3:

Input: adjList = []
Output: []
Explanation: This an empty graph, it does not have any nodes.



Constraints:

        • The number of nodes in the graph is in the range [0, 100].

        • 1 <= Node.val <= 100

        • Node.val is unique for each node.

        • There are no repeated edges and no self-loops in the graph.

• The Graph is connected and all nodes can be visited starting from
the given node.
"""

"""
# 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"]:
        oldToNew = {}

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

            copy = Node(node.val)
            oldToNew[node] = copy

            for n in node.neighbors:
                copy.neighbors.append(dfs(n))
            return copy

        return dfs(node) if node else None