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
         / \
         \_/

思路：1.clone nodes 2. clone nodes's neighbors 3. 利用HashMap 记录 旧节点 与 新clone节点的映射关系。
相关题目：copy random LinkedList

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     ArrayList<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    /**
     * @param node: A undirected graph node
     * @return: A undirected graph node
     */
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) {
            return null;
        }
        ArrayList<UndirectedGraphNode> nodes = new ArrayList<>();
        HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
        nodes.add(node);
        map.put(node, new UndirectedGraphNode(node.label));
        int start = 0;
        while (start < nodes.size()) {
            UndirectedGraphNode head = nodes.get(start++);
            for (int i = 0; i < head.neighbors.size(); i++) {
                UndirectedGraphNode neighbor = head.neighbors.get(i);
                if (!map.containsKey(neighbor)) {
                    map.put(neighbor, new UndirectedGraphNode(neighbor.label));
                    nodes.add(neighbor);
                }
            }
        }

        for (int i = 0; i < nodes.size(); i++) {
            UndirectedGraphNode newNode = map.get(nodes.get(i));
               for (int j = 0; j < nodes.get(i).neighbors.size(); j++) {
                   newNode.neighbors.add(map.get(nodes.get(i).neighbors.get(j)));
            }
        }
        return map.get(node);
    }
}