写的有点复杂，期待比较精妙的方法

1111ms通过

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int ai = in.nextInt();
        int m = in.nextInt();
        int[] memo = new int[n];
        memo[ai] = 1;
        Map<Integer, List<Integer>> records = new HashMap<>();
        for(int i = 0; i < m; i++) {
            String[] strs = in.next().split(",");
            int val1 = Integer.parseInt(strs[0]), val2 = Integer.parseInt(strs[1]);
            if(!records.containsKey(val1)) records.put(val1, new ArrayList<Integer>());
            if(!records.containsKey(val2)) records.put(val2, new ArrayList<Integer>());
            records.get(val1).add(val2);
            records.get(val2).add(val1);
        }
        int count = 0;
        Deque<Integer> queue = new ArrayDeque<>();
        queue.push(ai);
        while(!queue.isEmpty()){
            int size = queue.size();
            for(int i = 0; i < size; i++) {
                for(Integer num : records.get(queue.pop())) {
                    if(memo[num] == 0){
                        memo[num] = 1;
                        queue.push(num);
                        count++;
                    }
                }
            }
        }
        System.out.println(count - records.get(ai).size());
    }
}