#!/usr/bin/env python
# encoding: utf-8
"""
clone_graph.py

Created by Shengwei on 2014-07-13.
"""

# https://oj.leetcode.com/problems/clone-graph/
# tags: easy / medium, graph, hashtable, recursion, copy, dfs

"""
Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.


OJ's undirected graph serialization:
Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbor of the node.
As an example, consider the serialized graph {0,1,2#1,2#2,2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
Second node is labeled as 1. Connect node 1 to node 2.
Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.
Visually, the graph looks like the following:

       1
      / \
     /   \
    0 --- 2
         / \
         \_/
"""

# TODO: rewrite using stack instead of recurison

# Definition for a undirected graph node
# class UndirectedGraphNode:
#     def __init__(self, x):
#         self.label = x
#         self.neighbors = []

class Solution:
    # @param node, a undirected graph node
    # @return a undirected graph node
    def cloneGraph(self, root):
        if root is None:
            return None
        
        visited = {}
        def clone(node):
            if node in visited:
                return visited[node]
            
            copy = UndirectedGraphNode(node.label)
            visited[node] = copy
            for neighbor in node.neighbors:
                copy.neighbors.append(clone(neighbor))
            
            return copy
        
        return clone(root)
