clone graph.java

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null)
            return null;
        HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        LinkedList<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        queue.add(node);
        map.put(node, new UndirectedGraphNode(node.label));
        while (!queue.isEmpty()) {
            UndirectedGraphNode curr = queue.removeFirst();
            for (int i = 0; i < curr.neighbors.size(); i++) {
                if (!map.containsKey(curr.neighbors.get(i))) {
                    queue.add(curr.neighbors.get(i));
                    map.put(curr.neighbors.get(i), new UndirectedGraphNode(curr.neighbors.get(i).label));
                }
            }
        }
        HashSet<UndirectedGraphNode> visited = new HashSet<UndirectedGraphNode>();
        queue.add(node);
        visited.add(node);
        while (!queue.isEmpty()) {
            UndirectedGraphNode curr = queue.removeFirst();
            UndirectedGraphNode copy = map.get(curr);
            for (int i = 0; i < curr.neighbors.size(); i++) {
                copy.neighbors.add(map.get(curr.neighbors.get(i)));
                if (!visited.contains(curr.neighbors.get(i))) {
                    queue.add(curr.neighbors.get(i));
                    visited.add(curr.neighbors.get(i));
                }
            }
        }
        return map.get(node);
    }
}