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

// ต้องใช้ Java 5
public class WordCount {
   public static void main(String[] args) throws Exception {
      String fn = "2550.txt";
      BufferedReader fi = new BufferedReader(new FileReader(fn));      
      Map< String, Integer> wordCount = new TreeMap< String, Integer>();
      String line;

      while ((line = fi.readLine()) != null) {
         BreakIterator boundary =  BreakIterator.getWordInstance(new Locale("th"));
         boundary.setText(line);
         int start = boundary.first();
         int end = boundary.next();
         while (end != BreakIterator.DONE) {
            String word = line.substring(start, end).trim();
            if (!word.equals("")) {
               Integer c = wordCount.get(word);
               wordCount.put(word, new Integer(c == null ? 1 : (c + 1)));
            }
            start = end;
            end = boundary.next();
         }
      }
      fi.close();
      System.out.println(wordCount.toString());
   }
} 

ปี 40 มี 38334 คำ ปี 50 มี 45719 คำ มีความยาวของ LCS เป็น 19668 คำ

(LCS คงบอกอะไรไม่ได้มาก เพราะถ้ามีการสลับมาตราหรือหมวด จะได้ความยาวที่สั้นลง แต่อย่างน้อยก็บอก lower bound ของส่วนร่วม ความจริงน่าจะแยกหาตามหมวดตามมาตรา แต่เริ่มง่วงนอน...)

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

public class LLCS {
  public static void main(String[] args) throws IOException {
    String[] s2550 = getWords("2550.txt");
    String[] s2540 = getWords("2540.txt");
    System.out.println("2540 มี " + s2540.length + "คำ, 2550 มี " + s2550.length + "คำ");
    System.out.println("Length of LCS = " + llcs(s2540, s2550));
  }
  //-----------------------------------------------------
  static String[] getWords(String fn) throws IOException {
    BufferedReader fi = new BufferedReader(new FileReader(fn));
    String line;
    ArrayList< String> words = new ArrayList< String>();
    
    while ((line = fi.readLine()) != null) {
      BreakIterator boundary = BreakIterator.getWordInstance(new Locale("th"));
      boundary.setText(line);
      int start = boundary.first();
      int end = boundary.next();
      while (end != BreakIterator.DONE) {
        String word = line.substring(start, end).trim();
        if (!word.equals("")) {
          if (Character.isLetter(word.charAt(0))) words.add(word);
        }
        start = end;
        end = boundary.next();
      }
    }
    fi.close();
    return words.toArray(new String[0]);
  }
  //-----------------------------------------------------------
  static int llcs(String[] x, String[] y) {
    int[] L0 = new int[y.length + 1];
    int[] L1 = new int[y.length + 1];

    for (int j = 1; j < L0.length; j++) L0[j] = 0;
    for (int i = 0; i < x.length; i++) {
      L1[0] = 0;
      for (int j = 1; j < L1.length; j++) {
        if (x[i].equals(y[j - 1])) {
          L1[j] = 1 + L0[j - 1];
        } else {
          L1[j] = Math.max(L0[j], L1[j - 1]);
        }
      }
      if (i % 100 == 0) System.out.println(i);
      int[] t = L0; L0 = L1; L1 = t;
    }
    return L0[L0.length - 1];
  }
}