CloneGraph133.java

/**
 * 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 #.
 *
 * 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:
 *
 *        1
 *       / \
 *      /   \
 *     0 --- 2
 *          / \
 *          \_/
 *
 */

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */

public class CloneGraph133 {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        HashMap<Integer, UndirectedGraphNode> map = new HashMap<>();
        return clone(node, map);
    }

    private UndirectedGraphNode clone(UndirectedGraphNode node, HashMap<Integer, UndirectedGraphNode> map) {
        if (node == null) return null;

        if (map.containsKey(node.label)) {
            return map.get(node.label);
        }
        UndirectedGraphNode clone = new UndirectedGraphNode(node.label);
        map.put(clone.label, clone);
        for (UndirectedGraphNode neighbor : node.neighbors) {
            clone.neighbors.add(clone(neighbor, map));
        }
        return clone;
    }
}