JAVA沒法玩系列，C++寫了是248ms，JAVA 3000ms的時間限制都TLE，我已經看到考PAT的時候自己沮喪的樣子了。

簡單的BFS。

1 import java.util.*;  2 import java.io.*;  3   4 class FastReader{  5     BufferedReader reader;  6     StringTokenizer tokenizer;  7       8     FastReader(InputStream stream){  9         reader = new BufferedReader(new InputStreamReader(stream), 1 << 20); 10         tokenizer = null; 11     } 12      13     String next(){ 14         while (tokenizer == null || !tokenizer.hasMoreTokens()){ 15             try { 16                 tokenizer = new StringTokenizer(reader.readLine()); 17             } catch (Exception e){ 18                 throw new RuntimeException(e); 19             } 20         } 21          22         return tokenizer.nextToken(); 23     } 24      25     int next_int(){ 26         return Integer.parseInt(next()); 27     } 28 } 29  30 public class Main { 31     static ArrayList
     
      
       > graph; 32      33     static int bfs(int start, int level){ 34         int count = 0; 35         int level_cnt = 0; 36          37         Boolean[] visited = new Boolean[graph.size()]; 38         Arrays.fill(visited, false); 39          40         Queue
       
         cur_level = new LinkedList
        
         (); 41         cur_level.add(start); 42         visited[start] = true; 43          44         while (!cur_level.isEmpty()){ 45             Queue
         
           next_level = new LinkedList
          
           (); 46 47 while (!cur_level.isEmpty()){ 48 int cur_idx = cur_level.poll(); 49 50 for (Integer next_idx : graph.get(cur_idx)){ 51 if (visited[next_idx]) 52 continue; 53 54 next_level.add(next_idx); 55 visited[next_idx] = true; 56 count++; 57 } 58 } 59 60 level_cnt++; 61 if (level_cnt >= level) 62 break; 63 64 cur_level = next_level; 65 } 66 67 return count; 68 } 69 70 @SuppressWarnings("unused") 71 public static void main(String[] args){ 72 FastReader reader = new FastReader(System.in); 73 74 int N, L; 75 N = reader.next_int(); 76 L = reader.next_int(); 77 78 graph = new ArrayList
           
            
             >(); 79 for (int i = 0; i < N; i++) 80 graph.add(new ArrayList
             
              ()); 81 82 for (int i = 0; i < N; i++){ 83 int num = reader.next_int(); 84 85 for (int j = 0; j < num; j++){ 86 int idx = reader.next_int(); 87 graph.get(idx - 1).add(i); 88 } 89 } 90 91 int K = reader.next_int(); 92 ArrayList
              
                res_arr = new ArrayList
               
                (); 93 for (int i = 0; i < K; i++){ 94 int idx = reader.next_int(); 95 int res = bfs(idx - 1, L); 96 97 res_arr.add(res); 98 } 99 100 for (Integer res : res_arr){101 System.out.println(res);102 }103 }104 }
               
              
             
            
           
          
         
        
       
      
     

下面刷題都用C++了，感覺clang++的編譯報錯好萌啊...