Clone Graph [LeetCode]

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

         / \

         \_/

Summary: BFS, one queue for BFS, one map for visited nodes,  one map for mapping between original nodes and the nodes of new graph.

 1 /**

 2  * Definition for undirected graph.

 3  * struct UndirectedGraphNode {

 4  *     int label;

 5  *     vector<UndirectedGraphNode *> neighbors;

 6  *     UndirectedGraphNode(int x) : label(x) {};

 7  * };

 8  */

 9 class Solution {

10 public:

11     UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {

12         if(node == NULL)

13             return NULL;

14         vector<UndirectedGraphNode *> node_queue;

15         map<UndirectedGraphNode *, bool> visited;

16         map<UndirectedGraphNode *, UndirectedGraphNode *> node_map;

17         UndirectedGraphNode * root = new UndirectedGraphNode(node->label);

18         node_map[node] = root;

19         visited[node] = true;

20         node_queue.push_back(node);

21         

22         while(node_queue.size() > 0){

23             UndirectedGraphNode * node = node_queue[0];

24             node_queue.erase(node_queue.begin());

25             UndirectedGraphNode * new_node = node_map[node];

26             for(auto item : node->neighbors){

27                 if(visited.find(item) != visited.end()){

28                     new_node->neighbors.push_back(node_map[item]);

29                 }else{

30                     node_queue.push_back(item);

31                     UndirectedGraphNode * new_item = new UndirectedGraphNode(item->label);

32                     node_map[item] = new_item; 

33                     new_node->neighbors.push_back(new_item);

34                     visited[item] = true;

35                 }

36             }

37         }

38         

39         return root;

40     }

41 };