Clone Graph.java

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     ArrayList<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    /**
     * @param node: A undirected graph node
     * @return: A undirected graph node
     */
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        // write your code here
        if (node == null) {
            return null;
        }
        
        ArrayList<UndirectedGraphNode> nodes = new ArrayList<>();
        HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
        
        nodes.add(node);
        map.put(node, new UndirectedGraphNode(node.label));
        
        //clone node
        int start = 0;
        while (start < nodes.size()) {
            UndirectedGraphNode tempnode = nodes.get(start++);
            for (int i = 0; i < tempnode.neighbors.size(); i++) {
                if (map.containsKey(tempnode.neighbors.get(i))) {
                    continue;
                } else {
                    nodes.add(tempnode.neighbors.get(i));
                    map.put(tempnode.neighbors.get(i), new UndirectedGraphNode(tempnode.neighbors.get(i).label));
                }
            }
        }
        
        //clone neighbors
        for (int i = 0; i < nodes.size(); i++) {
            UndirectedGraphNode tempnode = nodes.get(i);
            UndirectedGraphNode cloneNode = map.get(tempnode);
            for (int j = 0; j < tempnode.neighbors.size(); j++) {
                cloneNode.neighbors.add(map.get(tempnode.neighbors.get(j)));
            }
        }
        
        return map.get(node);
    }
}