java 实现的Boyer-Moore(BM)算法，boyer-moorebm,BM算法是一种高效的单模

java 实现的Boyer-Moore(BM)算法，boyer-moorebm,BM算法是一种高效的单模

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

    import java.util.Arrays;      import java.util.HashMap;      import java.util.List;      import java.util.ArrayList;      import java.util.Map;      public class BoyerMoore {          public static List<Integer> match(String pattern, String text) {              List<Integer> matches = new ArrayList<Integer>();              int m = text.length();              int n = pattern.length();              Map<Character, Integer> rightMostIndexes = preprocessForBadCharacterShift(pattern);              int alignedAt = 0;              while (alignedAt + (n - 1) < m) {                  for (int indexInPattern = n - 1; indexInPattern >= 0; indexInPattern--) {                  int indexInText = alignedAt + indexInPattern;                  char x = text.charAt(indexInText);                  char y = pattern.charAt(indexInPattern);                      if (indexInText >= m) break;                      if (x != y) {                          Integer r = rightMostIndexes.get(x);                          if (r == null) {                              alignedAt = indexInText + 1;                          }                          else {                              int shift = indexInText - (alignedAt + r);                              alignedAt += shift > 0 ? shift : 1;                          }                          break;                      }                      else if (indexInPattern == 0) {                          matches.add(alignedAt);                          alignedAt++;                      }                  }              }              return matches;          }          private static Map<Character, Integer> preprocessForBadCharacterShift(                  String pattern) {              Map<Character, Integer> map = new HashMap<Character, Integer>();              for (int i = pattern.length() - 1; i >= 0; i--) {                  char c = pattern.charAt(i);                  if (!map.containsKey(c)) map.put(c, i);              }              return map;          }          public static void main(String[] args) {              List<Integer> matches = match("ana", "bananas");              for (Integer integer : matches) System.out.println("Match at: " + integer);              System.out.println((matches.equals(Arrays.asList(1, 3)) ? "OK" : "Failed"));          }      }