判断有向图中两点之间是否存在路径

对于一个有向图，请实现一个算法，找出两点之间是否存在一条路径。给定图中的两个结点的指针UndirectedGraphNode*a,UndirectedGraphNode* b(请不要在意数据类型，图是有向图),请返回一个bool，代表两点之间是否存在一条路径(a到b或b到a)。

import java.util.*;

/*
public class UndirectedGraphNode {
    int label = 0;
    UndirectedGraphNode left = null;
    UndirectedGraphNode right = null;
    ArrayList<UndirectedGraphNode> neighbors = new ArrayList<UndirectedGraphNode>();

    public UndirectedGraphNode(int label) {
        this.label = label;
    }
}*/
public class Path {
    
    ArrayList<UndirectedGraphNode> nodeList = new ArrayList<UndirectedGraphNode>();
    boolean hasLine = false;
    
    public boolean checkPath(UndirectedGraphNode a, UndirectedGraphNode b) {
        return hasPath(a, b) || hasPath(b, a);
    }
    
    public boolean hasPath(UndirectedGraphNode a, UndirectedGraphNode b){
        if(a == b || hasLine){
            hasLine = true;
            return true;
        }else{
            if(!nodeList.contains(a)){
                nodeList.add(a);
            }else{
                return false;
            }
        }
        
        for(int i = 0; i < a.neighbors.size(); i++){
            hasPath(a.neighbors.get(i), b);
        }
        
        return hasLine;
    }
}

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