解法一：倒排索引

遍历全部Book查找会非常慢，使用 Map 在单词和书本 id 之间建立倒排索引加速查找。

  1. import java.io.*;
  2. import java.util.*;
  4. public class Main {
  5.     public static void main(String[] args) throws IOException {
  6.         BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
  7.         PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
  8.         int N = Integer.parseInt(in.readLine());
  10.         Map<String, List<String>> titieMap = new HashMap<>();
  11.         Map<String, List<String>> authorMap = new HashMap<>();
  12.         Map<String, List<String>> keyWordMap = new HashMap<>();
  13.         Map<String, List<String>> publisherMap = new HashMap<>();
  14.         Map<Integer, List<String>> yearMap = new HashMap<>();
  16.         Book[] books = new Book[N];
  17.         for (int i = 0; i < N; ++i) {
  18.             books[i] = new Book(
  19.                     in.readLine(),
  20.                     in.readLine(),
  21.                     in.readLine(),
  22.                     in.readLine(),
  23.                     in.readLine(),
  24.                     Integer.parseInt(in.readLine())
  25.             );
  26.         }
  27.         Arrays.sort(books);
  28.         List<String> tmp;
  29.         for (Book book : books) {
  31.             tmp = titieMap.getOrDefault(book.title, new ArrayList<>());
  32.             tmp.add(book.id);
  33.             titieMap.put(book.title, tmp);
  35.             tmp = authorMap.getOrDefault(book.author, new ArrayList<>());
  36.             tmp.add(book.id);
  37.             authorMap.put(book.author, tmp);
  39.             for (String keyword : book.keyWords) {
  40.                 tmp = keyWordMap.getOrDefault(keyword, new ArrayList<>());
  41.                 tmp.add(book.id);
  42.                 keyWordMap.put(keyword, tmp);
  43.             }
  45.             tmp = publisherMap.getOrDefault(book.publisher, new ArrayList<>());
  46.             tmp.add(book.id);
  47.             publisherMap.put(book.publisher, tmp);
  49.             tmp = yearMap.getOrDefault(book.year, new ArrayList<>());
  50.             tmp.add(book.id);
  51.             yearMap.put(book.year, tmp);
  52.         }
  54.         int M = Integer.parseInt(in.readLine());
  55.         for (int i = 0; i < M; ++i) {
  56.             String query = in.readLine();
  57.             out.println(query);
  58.             String request = query.substring(3);
  59.             List<String> ans;
  60.             switch (query.charAt(0)) {
  61.                 case '1':
  62.                     ans = titieMap.get(request);
  63.                     break;
  64.                 case '2':
  65.                     ans = authorMap.get(request);
  66.                     break;
  67.                 case '3':
  68.                     ans = keyWordMap.get(request);
  69.                     break;
  70.                 case '4':
  71.                     ans = publisherMap.get(request);
  72.                     break;
  73.                 case '5':
  74.                     ans = yearMap.get(Integer.parseInt(request));
  75.                     break;
  76.                 default:
  77.                     ans = null;
  78.             }
  79.             if (ans == null) {
  80.                 out.println("Not Found");
  81.             } else {
  82.                 for (String s : ans) {
  83.                     out.println(s);
  84.                 }
  85.             }
  86.         }
  87.         out.flush();
  88.     }
  89. }
  91. class Book implements Comparable {
  92.     String id;
  93.     String title;
  94.     String author;
  95.     Set<String> keyWords;
  96.     String publisher;
  97.     int year;
  99.     Book(String id, String title, String author, String keyWords, String publisher, int year) {
  100.         this.id = id;
  101.         this.title = title;
  102.         this.author = author;
  103.         this.keyWords = new HashSet<>(Arrays.asList(keyWords.split(" ")));
  104.         this.publisher = publisher;
  105.         this.year = year;
  106.     }
  108.     @Override
  109.     public String toString() {
  110.         return "Book{" +
  111.                 "id=" + id +
  112.                 ", title='" + title + '\'' +
  113.                 ", author='" + author + '\'' +
  114.                 ", keyWords=" + keyWords +
  115.                 ", publisher='" + publisher + '\'' +
  116.                 ", year=" + year +
  117.                 '}';
  118.     }
  120.     @Override
  121.     public int compareTo(Object o) {
  122.         Book book = (Book) o;
  123.         return id.compareTo(book.id);
  124.     }
  125. }