133.Clone Graph

1-dfs + hashMap

拷贝图。图的遍历，主要就是DFS和BFS, 这道题考察基本功。需要注意的地点是如何建立visited数组

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if(node == null)
            return null;
        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
        return dfs(node, map);
    }

    public UndirectedGraphNode dfs(UndirectedGraphNode node, Map<UndirectedGraphNode, UndirectedGraphNode> map){
        if(node == null)
            return null;
        else if(map.containsKey(node)){
            return map.get(node);
        }
        else{
            UndirectedGraphNode cloneNode = new UndirectedGraphNode(node.label);
            map.put(node, cloneNode);
            for(UndirectedGraphNode neighbor : node.neighbors){
                cloneNode.neighbors.add(dfs(neighbor, map));
            }
            return cloneNode;
        }

    }
}