图的深拷贝 Clone Graph

问题：Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.

思路：图的复制/克隆问题。给你的只是图的冰山一角，就让你拷贝整张图。

第一步，先遍历(两种遍历方法)原图。把所有结点拿到手，构造一个邻接表头。

第二步，根据原图的邻接表头，重建一个新的邻接表头。

第三步，对于每个结点，顺序取得其邻接结点，并将克隆图中对应的结点指针加入到克隆图中对应的邻接表中。

为了访问方便，使用了哈希映射表 unorderd_map<结点label，结点指针> 来重构原图和新图。

代码：时间复杂度O(N)，空间复杂度O(N)。

/** * 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 == NULL)            return NULL;                    unordered_map<int, UndirectedGraphNode *> m; //origin graph        queue<UndirectedGraphNode *> q;        q.push(node);        while(!q.empty())        {            UndirectedGraphNode *tmp = q.front();            q.pop();                        if(m.find(tmp->label) == m.end())                m.insert(pair<int, UndirectedGraphNode *>(tmp->label, tmp));            for(int i=0;i < tmp->neighbors.size();i++)                if(m.find(tmp->neighbors[i]->label) == m.end())                    q.push(tmp->neighbors[i]);        }                unordered_map<int, UndirectedGraphNode *> clone; // clone graph        unordered_map<int, UndirectedGraphNode *>::iterator it = m.begin();        // Step 1: create new node         for(;it != m.end(); it++)        {            UndirectedGraphNode * temp = new UndirectedGraphNode((*it).first);            clone.insert(pair<int, UndirectedGraphNode *>((*it).first, temp));        }                // Step 2: fill the neighbors        it = m.begin();        for(;it != m.end(); it++)        {            for(int i=0;i<(*it).second->neighbors.size();i++)            {                clone[(*it).first]->neighbors.push_back( clone[(*it).second->neighbors[i]->label] );            }        }        return clone[node->label];    }  };