[LeetCode]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
         / \
         \_/

Analysis:

如果想在一次遍历中，完成拷贝的话，那就需要使用额外的内存来使用map存储源节点和拷贝节点之间的对应关系。有了这个关系之后，在遍历图的过程中，就可以同时处理访问节点及访问节点的拷贝节点，一次完成。
Java

public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node==null){
            return null;
        }
        HashMap<Integer, UndirectedGraphNode> checker=new HashMap<Integer, UndirectedGraphNode>();
        return clone(node, checker);
    }
    
    private UndirectedGraphNode clone (UndirectedGraphNode node, HashMap<Integer, UndirectedGraphNode> checker){
        if (checker.containsKey(node.label)){
            return checker.get(node.label);
        }
        
        UndirectedGraphNode newNode=new UndirectedGraphNode(node.label);
        checker.put(newNode.label,newNode);
        
        for (UndirectedGraphNode tempNode: node.neighbors){
 
            newNode.neighbors.add(clone(tempNode, checker));
        }
        
        return newNode;
    }

c++

UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if(node == NULL) return NULL;
    unordered_map<UndirectedGraphNode *, UndirectedGraphNode *>nodeMap;
    queue<UndirectedGraphNode *> visit;
    visit.push(node);
    UndirectedGraphNode * nodeCopy = new UndirectedGraphNode(node->label);
    nodeMap[node] = nodeCopy;
    while(visit.size()>0){
        UndirectedGraphNode * cur = visit.front();
        visit.pop();
        for(int i=0; i<cur->neighbors.size();i++){
            UndirectedGraphNode *neighb = cur->neighbors[i];
            if(nodeMap.find(neighb) == nodeMap.end()){
                UndirectedGraphNode *neighCopy = new UndirectedGraphNode(neighb->label);
                nodeMap[cur]->neighbors.push_back(neighCopy);
                nodeMap[neighb] = neighCopy;
                visit.push(neighb);
            }else{
                nodeMap[cur]->neighbors.push_back(nodeMap[neighb]);
            }
        }

    }
    return nodeCopy;
    }