21. Clone Graph

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 #.

1. First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
2. Second node is labeled as 1. Connect node 1 to node 2.
3. 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
         / \
         \_/

思想： 简单纯粹的深度优先搜索。 

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
 typedef UndirectedGraphNode NODE;
 typedef pair<NODE*, NODE*> PAIR;
 NODE* dfs(NODE *node, unordered_map<NODE*, NODE*> &_map) {
     if(_map.count(node)) return _map[node];
     NODE *p = new NODE(node->label);
     _map.insert(PAIR(node, p));
     for(size_t i = 0; i < node->neighbors.size(); ++i) {
         p->neighbors.push_back(dfs(node->neighbors[i], _map));
     }
     return p;
 }

class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        unordered_map<NODE*, NODE*> _map;
        _map[NULL] = NULL;
        return dfs(node, _map);
    }
};