133. Clone Graph

/*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         / \         \_/克隆图的一个难点就是一个结点的邻居可能在已经出现过，这样你只要把他的指针加到邻居集合中即可，也有可能这个结点还没出现过，因此你需要新建一个这个结点，因此我们需要一个hash表来对结点做一一映射每次搜索的时候看这个结点是不是已经被创建，是的话就返回其copy，否则就创建，然后再依次深度遍历其邻居结点并将其加入邻居集合中去．*//** * Definition for undirected graph. * struct UndirectedGraphNode { *     int label; *     vector<UndirectedGraphNode *> neighbors; *     UndirectedGraphNode(int x) : label(x) {}; * }; */class Solution {public:    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {        if(!node) return NULL;        unordered_map<UndirectedGraphNode*,UndirectedGraphNode*> mp;        return clone(node,mp);    }    UndirectedGraphNode *clone(UndirectedGraphNode *node,unordered_map<UndirectedGraphNode*,UndirectedGraphNode*>&mp){        if(!node) return NULL;        if(mp.find(node)!=mp.end())//查看节点是否已经生成            return mp[node];        mp[node]=new UndirectedGraphNode(node->label);        for(auto n : node->neighbors)            mp[node]->neighbors.push_back(clone(n,mp));        return mp[node];    }};