Clone Graph

只写了DFS递归版，以后复习时再写BFS，DFS非递归版，戳 参考链接。

public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if(node == null) return null;
        HashMap<UndirectedGraphNode, UndirectedGraphNode> map = 
			new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        UndirectedGraphNode cloneNode = new UndirectedGraphNode(node.label);
        map.put(node, cloneNode);
        dfs(map, node);
        return cloneNode;
    }
    
    private void dfs(HashMap<UndirectedGraphNode, UndirectedGraphNode> map, UndirectedGraphNode node) {
        if(node == null) return;
        for(UndirectedGraphNode neighbor : node.neighbors) {
            if(!map.containsKey(neighbor)) { //用map兼职check是否visit过。
                UndirectedGraphNode cloneNeighbor = new UndirectedGraphNode(neighbor.label);
                map.put(neighbor, cloneNeighbor);
                dfs(map, neighbor);
            }
            map.get(node).neighbors.add(map.get(neighbor)); //这句是精华，把cloneNeighor加进去
        }
    }
}