133. Clone Graph

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.

OJ's undirected graph serialization:

Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbor of the node.

As an example, consider the serialized graph {0,1,2#1,2#2,2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

1. First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
2. Second node is labeled as 1. Connect node 1 to node 2.
3. Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.

Visually, the graph looks like the following:

       1
      / \
     /   \
    0 --- 2
         / \
         \_/

 

public class Solution {
    public Node cloneGraph(Node node) {
        if (node == null) return null;

        Queue<Node> queue = new LinkedList<>();
        HashMap<Node, Node> map = new HashMap<>();

        queue.offer(node);
        map.put(node, new Node(node.val));

        int start = 0;
        while (!queue.isEmpty()) {
            Node head = queue.poll();
            for (Node neighbor : head.neighbors) {
                if (!map.containsKey(neighbor)) {
                    map.put(neighbor, new Node(neighbor.val));
                    queue.offer(neighbor);
                }
            }
        }
        // clone neighbors
        for (Node originalNode : map.keySet()) {
            Node copyNode = map.get(originalNode);
            for (Node neighbor : originalNode.neighbors) {
                copyNode.neighbors.add(map.get(neighbor));
            }
        }
        return map.get(node);
    }
}