133. Clone Graph( 克隆图)

题目链接：https://leetcode.com/problems/clone-graph/

Given a reference of a node in a connected undirected graph, return a deep copy (clone) of the graph. Each node in the graph contains a val (int) and a list (List[Node]) of its neighbors.

Example:

Input:
{"$id":"1","neighbors":[{"$id":"2","neighbors":[{"$ref":"1"},{"$id":"3","neighbors":[{"$ref":"2"},{"$id":"4","neighbors":[{"$ref":"3"},{"$ref":"1"}],"val":4}],"val":3}],"val":2},{"$ref":"4"}],"val":1}

Explanation:
Node 1's value is 1, and it has two neighbors: Node 2 and 4.
Node 2's value is 2, and it has two neighbors: Node 1 and 3.
Node 3's value is 3, and it has two neighbors: Node 2 and 4.
Node 4's value is 4, and it has two neighbors: Node 1 and 3.

Note:

1. The number of nodes will be between 1 and 100.
2. The undirected graph is a simple graph, which means no repeated edges and no self-loops in the graph.
3. Since the graph is undirected, if node p has node q as neighbor, then node q must have node p as neighbor too.
4. You must return the copy of the given node as a reference to the cloned graph.

思路一：

dfs：

AC 1ms 100% java:

/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> neighbors;

    public Node() {}

    public Node(int _val,List<Node> _neighbors) {
        val = _val;
        neighbors = _neighbors;
    }
};
*/
class Solution {
    Map<Integer,Node> map=new HashMap();
    public Node cloneGraph(Node node) {
        return clone(node);
    }
    public Node clone(Node node){
        if(node==null)
            return null;
        if(map.containsKey(node.val))
            return map.get(node.val);
        Node newNode=new Node(node.val,new ArrayList<Node>());
        map.put(node.val,newNode);
        for(Node neighbor:node.neighbors){
            newNode.neighbors.add(clone(neighbor));
        }
        return newNode;
    }
}

方法二：BFS

/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> neighbors;

    public Node() {}

    public Node(int _val,List<Node> _neighbors) {
        val = _val;
        neighbors = _neighbors;
    }
};
*/
class Solution {
    public Node cloneGraph(Node node) {
        if(node==null)
            return null;
        Queue<Node> queue=new LinkedList();
        queue.add(node);
        Map<Node,Node> map=new HashMap();
        map.put(node,new Node(node.val,new ArrayList<Node>()));
        while(!queue.isEmpty()){
            Node temp=queue.poll();
            for(Node neighbor:temp.neighbors){
                if(!map.containsKey(neighbor)){
                    map.put(neighbor,new Node(neighbor.val,new ArrayList<Node>()));
                    queue.add(neighbor);
                }
                map.get(temp).neighbors.add(map.get(neighbor));
            }
        }
        return map.get(node);
    }
}