Clone Graph, Leetcode 解题笔记

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
/ \
\_/

这道题不是很难,但是需要非常细心。用一个Queue来进行BFS,并用一个map来映射新node和旧node。对于每个旧node的邻居,新建一个与这个邻居相同的node,并把它加入与这个旧node对应的新node的neighbor list中。

/**
 * 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;
        LinkedList<UndirectedGraphNode> q = new LinkedList<UndirectedGraphNode>();
        HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);
        q.add(node);
        map.put(node, newNode);
        while(q.size() != 0){
            UndirectedGraphNode cur = q.pop();
            for(UndirectedGraphNode n: cur.neighbors){
                if(!map.containsKey(n)){
                    UndirectedGraphNode copy = new UndirectedGraphNode(n.label);
                    map.put(n, copy);
                    map.get(cur).neighbors.add(copy);
                    q.add(n);
                }
                else{
                    map.get(cur).neighbors.add(map.get(n));
                }
            }
        }
        return newNode;
    }
}
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