CloneGraph.java

/**
 * Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.
 *
 * <p>OJ's undirected graph serialization: Nodes are labeled uniquely.
 *
 * <p>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}.
 *
 * <p>The graph has a total of three nodes, and therefore contains three parts as separated by #.
 *
 * <p>First node is labeled as 0. Connect node 0 to both nodes 1 and 2. Second node is labeled as 1.
 * Connect node 1 to node 2. 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:
 *
 * <p>1 / \ / \ 0 --- 2 / \ \_/
 */

import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.Queue;
import java.util.Set;

public class CloneGraph {
  public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
    if (node == null) return node;
    Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
    queue.add(node);
    Set<UndirectedGraphNode> visited = new HashSet<UndirectedGraphNode>();
    Map<UndirectedGraphNode, UndirectedGraphNode> map =
        new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
    while (!queue.isEmpty()) {
      UndirectedGraphNode n = queue.remove();
      if (visited.contains(n)) continue;
      visited.add(n);
      UndirectedGraphNode clone;
      if (!map.containsKey(n)) {
        clone = new UndirectedGraphNode(n.label);
        map.put(n, clone);
      } else {
        clone = map.get(n);
      }
      for (UndirectedGraphNode child : n.neighbors) {
        queue.add(child);
        UndirectedGraphNode cloneChild;
        if (!map.containsKey(child)) {
          cloneChild = new UndirectedGraphNode(child.label);
          map.put(child, cloneChild);
        } else {
          cloneChild = map.get(child);
        }
        clone.neighbors.add(cloneChild);
      }
    }
    return map.get(node);
  }
}