public class InvertedIndex {
            Map<String, List<Tuple>> index =
              new HashMap<String, List<Tuple>>(); //詞和這個(gè)詞在文檔中出現(xiàn)的位置信息


            // 索引文檔
            public void indexDoc(String docName, ArrayList<String> words) {
                int pos = 0;
                for (String word : words) {
                    pos++; // 位置
                    List<Tuple> idx = index.get(word);
                    if (idx == null) {
                        idx = new LinkedList<Tuple>();
                        index.put(word, idx);
                    }
                    idx.add(new Tuple(docName, pos));
                    System.out.println("indexed " + docName + " : " + pos + " words");
                }
            }


            // 搜索
            public void search(List<String> words) {
            for (String word : words) {
                Set<String> answer = new HashSet<String>();
                List<Tuple> idx = index.get(word);
                if (idx ! = null) {
                    for (Tuple t : idx) { //找到了一些文檔
                        answer.add(t.docName);
                    }
                }
                System.out.print(word);
                for (String f : answer) {
                    System.out.print(" " + f); //輸出文件名
                }
                System.out.println("");
            }
        }


        private class Tuple { //<文檔名，位置>元組
            private String docName; // 文檔名
            private int position; // 位置


            public Tuple(String d, int position) {
                this.docName = d;
                this.position = position;
            }
        }
    }

        public class Span {
            public int start; // 開(kāi)始位置
            public int end; // 結(jié)束位置


            public Span(int s, int e) {
                start = s;
                end = e;
            }


            public int length() {
                return end - start + 1;
            }


            public String toString() {
                return start + "-" + end;
            }
        }

        /** 一個(gè)索引應(yīng)該實(shí)現(xiàn)的功能模板 */
        public interface Index {
            /** 使用數(shù)據(jù)庫(kù)統(tǒng)計(jì)類(lèi)構(gòu)建索引 */
            public void build(DatabaseStatistics s);


            /** 從文件加載倒排索引 */
            public void read(String filename) throws IOException;


            /** 把內(nèi)存中建好的倒排索引存入文件 */
            public void flush(String filename) throws IOException;
        }