程序員面試金典題解 有向路徑檢查

題目描述

對於一個有向圖，請實現一個算法，找出兩點之間是否存在一條路徑。
給定圖中的兩個結點的指針UndirectedGraphNode* a,UndirectedGraphNode* b(請不要在意數據類型，圖是有向圖),請返回一個bool，代表兩點之間是否存在一條路徑(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 {
    public boolean checkPath(UndirectedGraphNode a, UndirectedGraphNode b) {
        return check(a,b)||check(b,a);
    }
    private boolean check(UndirectedGraphNode a, UndirectedGraphNode b){
        if(a == null || b == null){
            return false;
        }else if(a == b){
            return true;
         }
        LinkedList<UndirectedGraphNode> q=new LinkedList();
        ArrayList<UndirectedGraphNode> checkedMap = new ArrayList<UndirectedGraphNode>();
        q.add(a);
        checkedMap.add(a);
        while(!q.isEmpty()){
            UndirectedGraphNode node=q.poll();
            for(UndirectedGraphNode temp:node.neighbors){
                if(!checkedMap.contains(temp)){
                    if(temp==b){
                        return true;
                    }else{
                        checkedMap.add(temp);
                        q.add(temp);
                    }
                }
            }
        }
        return false;
    }
}