leetcode [133]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.

题目大意：

将给定的图进行深复制，这是一个无向图。

解法：

使用两个map,一个保存着原来的value到node的映射，一个保存着现在的新的图value到node的映射。

首先将图所有的node新建之后，再根据原来的node的neighbor去初始化现在新的node的neighbor。

java:

class Solution {
    private Map<Integer,Node>m=new HashMap<>();
    private Map<Integer,Node>order=new HashMap<>();

    private void helper(Node node){
        if(m.containsKey(node.val)) return;
        Node newNode=new Node(node.val,new ArrayList<>());
        m.put(node.val,newNode);
        order.put(node.val,node);
        for(Node neighbor:node.neighbors){
            helper(neighbor);
        }
    }

    public Node cloneGraph(Node node) {
        helper(node);
        for(Map.Entry<Integer,Node> entry:order.entrySet()){
            for(Node n:entry.getValue().neighbors){
                m.get(entry.getKey()).neighbors.add(m.get(n.val));
            }
        }

        return m.get(node.val);
    }
}