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:

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

Solution

DFS Graph

Complexity

O(N) O(N)

Code

/*
// 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;
        return clone(node, new HashMap<Node, Node>());
    }
    
    public Node clone(Node node, Map<Node, Node> map){
        if(map.containsKey(node))
            return map.get(node);

        Node newNode = new Node(node.val, new ArrayList<>());
        map.put(node, newNode);
        
        for(Node n : node.neighbors){
            newNode.neighbors.add(clone(n, map));
        }
        return newNode; 
    }
    
}