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
         / \
         \_/ 

/**
 * 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 *> map;
        queue<UndirectedGraphNode *> que;
        que.push(node);
        map[node] = new UndirectedGraphNode(node->label);
        while(!que.empty()) {
            UndirectedGraphNode *current = que.front();
            que.pop();
           
            for(auto iter : current->neighbors) {
                if (map.find(iter) == map.end()) {
                    map[iter] = new UndirectedGraphNode(iter->label);
                    que.push(iter);
                }

                map[current]->neighbors.push_back(map[iter]);
            }
        }
        return map[node];
    }
};

 
class Solution {
public:
    void BFS(UndirectedGraphNode *node, unordered_map<UndirectedGraphNode *, UndirectedGraphNode *> &map)
    { 
        if (map[node]) return;         map[node] = new UndirectedGraphNode(node->label);
        
        for(UndirectedGraphNode *child : node->neighbors)
            BFS(child, map);
    }
    
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (!node) return NULL;
        unordered_map<UndirectedGraphNode *, UndirectedGraphNode *> map;
        BFS(node, map); 
        
        for(auto iter:map)
            for(UndirectedGraphNode *child : iter.first->neighbors)
                iter.second->neighbors.push_back(map[child]);
        
        return map[node];
    }
};

 
class Solution {
public:
    UndirectedGraphNode *DFS(UndirectedGraphNode *node, unordered_map<UndirectedGraphNode *, UndirectedGraphNode *> &map)
    { 
        if (map[node]) return map[node]; 
        
        UndirectedGraphNode *nn = new UndirectedGraphNode(node->label);
        map[node] = nn;
        
        for(UndirectedGraphNode *child : node->neighbors)
            nn->neighbors.push_back(DFS(child, map));
            
        return nn;
    }
    
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (!node) return NULL;
        unordered_map<UndirectedGraphNode *, UndirectedGraphNode *> map;
        return DFS(node, map); 
    }
};