Clone Graph

Leetcode

題意：

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
         / \
         \_/

解題思路：

使用dfs加hashmap來作，程式碼如下：

/**
 * 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 (node == null) {
            return null;
        }

        HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        HashSet<UndirectedGraphNode> visited = new HashSet<UndirectedGraphNode>();
        Queue<UndirectedGraphNode> q = new LinkedList<UndirectedGraphNode>();

        q.offer(node);
        visited.add(node);
        map.put(node, new UndirectedGraphNode(node.label));
        while (!q.isEmpty()) {
            UndirectedGraphNode cur = q.poll();
            List<UndirectedGraphNode> neighbors = cur.neighbors;
            for (UndirectedGraphNode neighbor : neighbors) {
                if (!visited.contains(neighbor)) {
                    visited.add(neighbor);
                    UndirectedGraphNode newNeighbor = new UndirectedGraphNode(neighbor.label);
                    map.put(neighbor, newNeighbor);
                    q.offer(neighbor);

                }
                map.get(cur).neighbors.add(map.get(neighbor));
            }
        }

        return map.get(node);

    }
}