类似于二叉树的三种遍历，我们可以基于遍历的模板做很多额外的事情，图的两种遍历，深度和广度模板同样也可以做很多额外的事情，这里举例利用深度优先遍历的模板来进行复制，深度优先中，我们先访问第一个结点，接着访问第一个邻接点，再访问邻节点的邻节点。。。。

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):
        if None == node:
            return None
        #访问当前点，这里不是简单的print，而是复制，若已经复制，则返回副本
        if nodeMap.has_key(node):
            return nodeMap[node]
        #若没有副本，则复制一份，同样处理其邻接点
        else:
            clone = UndirectedGraphNode(node.label)
            nodeMap[node] = clone
            #访问其邻居节点
            for neighbor in node.neighbors:
                clone.neighbors.append(self.cloneNode(neighbor, nodeMap))
        return clone

Copy List with Random Pointer

class Solution:
    # @param head, a RandomListNode
    # @return a RandomListNode
    def copyRandomList(self, head):
        if None == head: return None
        nodeMap = {}
        return self.copyListNode(head, nodeMap)
        
    def copyListNode(self, node, nodeMap):
        if None == node: return None
        if nodeMap.has_key(node):
            return nodeMap[node]
        else: 
            cpNode = RandomListNode(node.label)
            nodeMap[node] = cpNode
            cpNode.next = self.copyListNode(node.next, nodeMap)
            cpNode.random = self.copyListNode(node.random, nodeMap)
        return cpNode