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
         / \
         \_/

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

/*
Use Queue to implement BFS and use HashMap to deep clone every graph node and connect their neighbors.

time:O(V+E), space:O(V), E is the number of neighbors, V is the number of nodes.
*/

public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) {
            return null;
        }
        Queue<UndirectedGraphNode> queue = new LinkedList<>();
        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
        queue.offer(node);
        map.put(node, new UndirectedGraphNode(node.label));
        while (!queue.isEmpty()) {
            UndirectedGraphNode curr = queue.poll();
            for (UndirectedGraphNode neighbor : curr.neighbors) {
                if (!map.containsKey(neighbor)) {
                    queue.offer(neighbor);
                    map.put(neighbor, new UndirectedGraphNode(neighbor.label));
                }
                map.get(curr).neighbors.add(map.get(neighbor));
            }
        }
        return map.get(node);
    }
}


//DFS, time:O(V+E), space:O(V)
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
        return deepClone(map, node);
    }
    public UndirectedGraphNode deepClone(Map<UndirectedGraphNode,                                              UndirectedGraphNode> map, UndirectedGraphNode node) {
        if (node == null) {
            return null;
        }
        if (map.containsKey(node)) {
            return map.get(node);
        }
        map.put(node, new UndirectedGraphNode(node.label)); 
        for (UndirectedGraphNode neighbor : node.neighbors) {
            map.get(node).neighbors.add(deepClone(map, neighbor));
        }
        return map.get(node);
    }

}