java 实现的Boyer-Moore(BM)算法

BM算法是一种高效的单模查找算法，可以加大查找步长，效率很高, 这是java实现的版本

1. import java.util.Arrays;
2. import java.util.HashMap;
3. import java.util.List;http://www.kmnk03.com/hxpfk/ylb/272.html
4. import java.util.ArrayList;
5. import java.util.Map;
6. http://www.kmnk03.com/hxpfk/bdf/264.html
7. public class BoyerMoore {
8. public static List<Integer> match(String pattern, String text) {
9. List<Integer> matches = new ArrayList<Integer>();
10. int m = text.length();
11. int n = pattern.length();
12. Map<Character, Integer> rightMostIndexes = preprocessForBadCharacterShift(pattern);
13. int alignedAt = 0;http://www.kmnk03.com/hxpfk/qcd/265.html
14. while (alignedAt + (n - 1) < m) {
15. for (int indexInPattern = n - 1; indexInPattern >= 0; indexInPattern--) {
16. int indexInText = alignedAt + indexInPattern;
17. char x = text.charAt(indexInText);
18. char y = pattern.charAt(indexInPattern);
19. if (indexInText >= m) break;
20. if (x != y) {http://www.kmnk03.com/hxpfk/qcd/266.html
21. Integer r = rightMostIndexes.get(x);
22. if (r == null) {
23. alignedAt = indexInText + 1;
24. }
25. else {http://www.kmnk03.com/hxpfk/pfsy/268.html
26. int shift = indexInText - (alignedAt + r);
27. alignedAt += shift > 0 ? shift : 1;
28. }
29. break;
30. }
31. else if (indexInPattern == 0) {
32. matches.add(alignedAt);
33. alignedAt++;http://www.kmnk03.com/hxpfk/ylb/271.html
34. }
35. }
36. }
37. return matches;
38. }http://www.kmnk03.com/hxpfk/xmz/269.html
39. private static Map<Character, Integer> preprocessForBadCharacterShift(
40. String pattern) {
41. Map<Character, Integer> map = new HashMap<Character, Integer>();
42. for (int i = pattern.length() - 1; i >= 0; i--) {
43. char c = pattern.charAt(i);
44. if (!map.containsKey(c)) map.put(c, i);
45. }
46. return map;
47. }http://www.kmnk03.com/hxpfk/qcd/267.html
48. public static void main(String[] args) {http://www.kmnk03.com/hxpfk/tf/270.html
49. List<Integer> matches = match("ana", "bananas");
50. for (Integer integer : matches) System.out.println("Match at: " + integer);
51. System.out.println((matches.equals(Arrays.asList(1, 3)) ? "OK" : "Failed"));
52. }http://www.kmnk03.com/hxpfk/npx/273.html
53. }kmnk03.com   www.kmnk03.com