要明白的基礎知識

node1=UndirectedGraphNode(1)
node2=UndirectedGraphNode(2)
nodeMap={}
nodeMap[node1]="hello"
nodeMap[node2]="world"
#這樣是合法的，列印nodeMap看看
nodeMap
Out[8]: 
{<__main__.UndirectedGraphNode at 0x18215e262e8>: 'world',
 <__main__.UndirectedGraphNode at 0x18215e26320>: 'hello'}

clone graph

考察最基本的圖的遍歷，深度遍歷和寬度遍歷 題目如下： Given the head of a graph, return a deep copy (clone) of the graph. Each node in the graph contains a label (int) and a list (List[UndirectedGraphNode]) of its neighbors. There is an edge between the given node and each of the nodes in its neighbors.

OJ’s undirected graph serialization (so you can understand error output): 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
     / \
     \_/

Note: The information about the tree serialization is only meant so that you can understand error output if you get a wrong answer. You don’t need to understand the serialization to solve the problem. DFS解法：

#深度優先遍歷解法
# 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 None == node: return None
        nodeMap = {}
        return self.cloneNode(node, nodeMap)

    def cloneNode(self, node, nodeMap):#注意理解這個函式的意思，就是clone一個node
        if None == node:
            return None
        #訪問當前點，這裡不是簡單的print，而是複製，若已經複製，即這個node已經被建立，則返回副本
        if node in nodeMap.keys():#node
            return nodeMap[node]
        #若沒有副本，則複製一份，同樣處理其鄰接點
        else:
            clone = UndirectedGraphNode(node.label)
            nodeMap[node] = clone
            #訪問其鄰居節點
            for neighbor in node.neighbors:
                clone.neighbors.append(self.cloneNode(neighbor, nodeMap))
        return clone