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 = []


# BFS
def cloneGraph1(self, node):
    if not node:
        return
    nodeCopy = UndirectedGraphNode(node.label)
    dic = {node: nodeCopy}
    queue = collections.deque([node])
    while queue:
        node = queue.popleft()
        for neighbor in node.neighbors:
            if neighbor not in dic: # neighbor is not visited
                neighborCopy = UndirectedGraphNode(neighbor.label)
                dic[neighbor] = neighborCopy
                dic[node].neighbors.append(neighborCopy)
                queue.append(neighbor)
            else:
                dic[node].neighbors.append(dic[neighbor])
    return nodeCopy

# DFS iteratively
def cloneGraph2(self, node):
    if not node:
        return
    nodeCopy = UndirectedGraphNode(node.label)
    dic = {node: nodeCopy}
    stack = [node]
    while stack:
        node = stack.pop()
        for neighbor in node.neighbors:
            if neighbor not in dic:
                neighborCopy = UndirectedGraphNode(neighbor.label)
                dic[neighbor] = neighborCopy
                dic[node].neighbors.append(neighborCopy)
                stack.append(neighbor)
            else:
                dic[node].neighbors.append(dic[neighbor])
    return nodeCopy

# DFS recursively
def cloneGraph(self, node):
    if not node:
        return
    nodeCopy = UndirectedGraphNode(node.label)
    dic = {node: nodeCopy}
    self.dfs(node, dic)
    return nodeCopy

def dfs(self, node, dic):
    for neighbor in node.neighbors:
        if neighbor not in dic:
            neighborCopy = UndirectedGraphNode(neighbor.label)
            dic[neighbor] = neighborCopy
            dic[node].neighbors.append(neighborCopy)
            self.dfs(neighbor, dic)
        else:
            dic[node].neighbors.append(dic[neighbor])