133. Clone Graph.py

# 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
#          / \
#          \_/

# 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, node):
        if not node:
            return None
        # save node
        # we need to put its neighbors to root which is only copy its label
        root = UndirectedGraphNode(node.label)
        queue = [node]
        visited = {}
        visited[node.label] = root
        while queue:
            parent = queue.pop(0)
            for children in parent.neighbors:
                
                if children.label not in visited:
                    queue.append(children)
                    visited[children.label] = UndirectedGraphNode(children.label)
                # save root's neighbor
                visited[parent.label].neighbors.append(visited[children.label])
                
        return root