133. Clone Graph

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    unordered_map<UndirectedGraphNode *,UndirectedGraphNode *> m;
    unordered_set<UndirectedGraphNode *> visited;
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (node == NULL)   return NULL;
        dfs_create(node);
        dfs_link(node);
        return m[node];
    }
    void dfs_create(UndirectedGraphNode *node) {
        if (node == NULL || m.count(node))   return;
        UndirectedGraphNode *p = new UndirectedGraphNode(node->label);
        m[node] = p;
        for (auto n : node->neighbors)
            dfs_create(n);
    }
    void dfs_link(UndirectedGraphNode *node) {
        if (node == NULL || visited.count(node))   return;
        visited.insert(node);
        for (auto n : node->neighbors) {
            m[node]->neighbors.push_back(m[n]);
            dfs_link(n);
        }
    }
};