133. Clone Graph

133. Clone Graph

Medium

Given the head of a graph, return a deep copy (clone) of the graph. Each node in the graph contains a label (int) and a list (List[UndirectedGraphNode]) of its neighbors. There is an edge between the given node and each of the nodes in its neighbors.

OJ's undirected graph serialization (so you can understand error output):

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
         / \
         \_/

Note: The information about the tree serialization is only meant so that you can understand error output if you get a wrong answer. You don't need to understand the serialization to solve the problem.

/**
 * 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 (null == node) {
            return null;
        }
        
        Queue<UndirectedGraphNode> queue = new ArrayDeque<>();
        queue.add(node);
        Map<Integer, UndirectedGraphNode> nodes = new HashMap<>();
        Map<Integer, UndirectedGraphNode> copyNodes = new HashMap<>();
        
        while (!queue.isEmpty()) {
            UndirectedGraphNode tNode = queue.poll();
            nodes.put(tNode.label, tNode);
            copyNodes.put(tNode.label, new UndirectedGraphNode(tNode.label));
            for (UndirectedGraphNode n: tNode.neighbors) {
                if (!nodes.containsKey(n.label)) {
                    queue.add(n);
                }
            }
        }
        
        for (Map.Entry<Integer, UndirectedGraphNode> entry: nodes.entrySet()) {
            for (UndirectedGraphNode n : entry.getValue().neighbors) {
                copyNodes.get(entry.getKey()).neighbors.add(copyNodes.get(n.label));
            }
        }
        
        return copyNodes.get(node.label);
    }
}