【LeetCode】Clone Graph 解题报告

【题目】

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】

这道题主要是数据结构的应用吧，用一个队列存放图中还未被访问的结点，用一个map存放克隆的新结点。对于队列中的结点，访问其邻居，如果该邻居已经被克隆，那么只需维护克隆结点之间的邻居关系即可，如果该邻居尚未被克隆，那么需要new一个新的结点作为它的克隆，并维护克隆后的邻居关系。

【Java代码】

/** * 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;                UndirectedGraphNode clone = new UndirectedGraphNode(node.label);                //用一个Map来保存已经克隆的新结点        HashMap<Integer, UndirectedGraphNode> map = new HashMap<Integer, UndirectedGraphNode>();        map.put(node.label, clone);                //用一个队列来保存没有访问过的结点        LinkedList<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();        queue.add(node);                while (!queue.isEmpty()) {            UndirectedGraphNode originalnode = queue.remove();            UndirectedGraphNode clonenode = map.get(originalnode.label);                        for (int i = 0; i < originalnode.neighbors.size(); i++) {                UndirectedGraphNode neighbor = originalnode.neighbors.get(i);                                //如果该邻居结点已被克隆                if (map.get(neighbor.label) != null) {                    clonenode.neighbors.add(map.get(neighbor.label));                    continue;                }                                //把该邻居放入queue中                queue.add(neighbor);                                //克隆该邻居结点                UndirectedGraphNode newnode = new UndirectedGraphNode(neighbor.label);                                //把新结点放入map中                map.put(neighbor.label, newnode);                                //把新结点加入邻居集中                clonenode.neighbors.add(newnode);            }        }                return clone;    }}