PAT 1076

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<ArrayList<Integer>> 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<Integer> cur_level = new LinkedList<Integer>();
 41         cur_level.add(start);
 42         visited[start] = true;
 43
 44         while (!cur_level.isEmpty()){
 45             Queue<Integer> next_level = new LinkedList<Integer>();
 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<ArrayList<Integer>>();
 79         for (int i = 0; i < N; i++)
 80             graph.add(new ArrayList<Integer>());
 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<Integer> res_arr = new ArrayList<Integer>();
 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...