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。

import java.util.*;
import java.io.*;

class FastReader{
    BufferedReader reader;
    StringTokenizer tokenizer;
    
    FastReader(InputStream stream){
        reader = new BufferedReader(new InputStreamReader(stream), 1 << 20);
        tokenizer = null;
    }
    
    String next(){
        while (tokenizer == null || !tokenizer.hasMoreTokens()){
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (Exception e){
                throw new RuntimeException(e);
            }
        }
        
        return tokenizer.nextToken();
    }
    
    int next_int(){
        return Integer.parseInt(next());
    }
}

public class Main {
    static ArrayList<ArrayList<Integer>> graph;
    
    static int bfs(int start, int level){
        int count = 0;
        int level_cnt = 0;
        
        Boolean[] visited = new Boolean[graph.size()];
        Arrays.fill(visited, false);
        
        Queue<Integer> cur_level = new LinkedList<Integer>();
        cur_level.add(start);
        visited[start] = true;
        
        while (!cur_level.isEmpty()){
            Queue<Integer> next_level = new LinkedList<Integer>();
            
            while (!cur_level.isEmpty()){
                int cur_idx = cur_level.poll();
                
                for (Integer next_idx : graph.get(cur_idx)){
                    if (visited[next_idx])
                        continue;
                    
                    next_level.add(next_idx);
                    visited[next_idx] = true;
                    count++;
                }
            }
            
            level_cnt++;
            if (level_cnt >= level)
                break;
            
            cur_level = next_level;
        }
        
        return count;
    }
    
    @SuppressWarnings("unused")
    public static void main(String[] args){
        FastReader reader = new FastReader(System.in);
        
        int N, L;
        N = reader.next_int();
        L = reader.next_int();
        
        graph = new ArrayList<ArrayList<Integer>>();
        for (int i = 0; i < N; i++)
            graph.add(new ArrayList<Integer>());
        
        for (int i = 0; i < N; i++){
            int num = reader.next_int();
            
            for (int j = 0; j < num; j++){
                int idx = reader.next_int();
                graph.get(idx - 1).add(i);
            }
        }
        
        int K = reader.next_int();
        ArrayList<Integer> res_arr = new ArrayList<Integer>();
        for (int i = 0; i < K; i++){
            int idx = reader.next_int();
            int res = bfs(idx - 1, L);
            
            res_arr.add(res);
        }
        
        for (Integer res : res_arr){
            System.out.println(res);
        }
    }
}

下面刷題都用C++了，感覺clang++的編譯報錯好萌啊...