Leetcode133-cloneGraph

Description

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.

Solution

/*
// 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 node;
        HashMap<Integer, Node> map = new HashMap<>();
        return clone(node, map);
    }
    
    private Node clone(Node node, HashMap<Integer, Node> map){
        if (node == null) return null;
        
        if (map.containsKey(node.val)) return map.get(node.val);
        
        List<Node> newNeighbors = new ArrayList<>();
        Node newNode = new Node(node.val, newNeighbors);
        map.put(node.val, newNode);
        
        for (Node n: node.neighbors){
            newNode.neighbors.add(clone(n, map));
        }
        
        return newNode;
    }
}

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