Clone Graph——LeetCode

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

         / \

         \_/

题目大意是给定一个无向图，可能有环，实现一个方法，deep clone这个图。

我的做法是采用BFS，从一个点开始，遍历它的邻居，然后加入队列，当队列非空，循环遍历，因为label是唯一的，采用map保存新生成的node，用label作为key。另外使用visited数组保存是否加入过队列，以免重复遍历。

Talk is cheap>>

　　public UndirectedGraphNode cloneGraph(UndirectedGraphNode root) {

        HashSet<Integer> visited = new HashSet<>();

        if (root==null)

            return null;

        List<UndirectedGraphNode> queue = new ArrayList<>();

        HashMap<Integer,UndirectedGraphNode> map = new HashMap<>();

        queue.add(root);

        while (!queue.isEmpty()) {

            UndirectedGraphNode node = queue.get(0);

            if (map.get(node.label)==null) {

                map.put(node.label, new UndirectedGraphNode(node.label));

            }

            UndirectedGraphNode tmp = map.get(node.label);

            queue.remove(0);

         

            for (int i = 0; i < node.neighbors.size(); i++) {

                int key = node.neighbors.get(i).label;

                if (map.get(key)==null){

                    map.put(key,new UndirectedGraphNode(key));

                }

                tmp.neighbors.add(map.get(key));

                visited.add(node.label);

                if (!visited.contains(key)){

                    queue.add(node.neighbors.get(i));

                    visited.add(key);

                }

            }

        }

        return map.get(root.label);

    }