Boyer-Moore算法

转自:grep之字符串搜索算法Boyer-Moore由浅入深（比KMP快3-5倍）

public class Solution {public String strStr(String haystack, String needle) {int begin = bm(haystack, needle);return begin == -1 ? null : haystack.substring(begin);}int bm(String str, String pattern) {if (pattern == null || pattern.length() == 0)return 0;int slen = str.length(), plen = pattern.length();char[] sarr = str.toCharArray(), parr = pattern.toCharArray();// pretreatmentint[] bmBc = preBmBc(parr);int[] bmGs = preBmGs(parr);// findint i, j = 0;while (j <= slen - plen) {for (i = plen - 1; i >= 0 && parr[i] == sarr[i + j]; i--);if (i < 0) { // findreturn j;} else {j += Math.max(bmBc[sarr[i + j]] - (plen - 1 - i), bmGs[i]);}}return -1;}// bad char heuristicint[] preBmBc(char[] pattern) {int m = pattern.length;int[] bmBc = new int[256];for (int i = 0; i < 256; i++) {bmBc[i] = m;}// set the rightest index of character pattern[i]for (int i = 0; i < m - 1; i++) {bmBc[pattern[i]] = m - 1 - i;}return bmBc;}// good suffix heuristicint[] preBmGs(char[] pattern) {int m = pattern.length;int[] bmGs = new int[m];int[] suff = suffix(pattern);// case 3: not matchfor (int i = 0; i < m; i++) {bmGs[i] = m;}// case 2: partial match suffixint j = 0;for (int i = m - 1; i >= 0; i--) {if (suff[i] == i + 1) {for (; j < m - 1 - i; j++) {if (bmGs[j] == m)bmGs[j] = m - 1 - i;}}}// case 1: match suffixfor (int i = 0; i <= m - 2; i++) {bmGs[m - 1 - suff[i]] = m - 1 - i;}return bmGs;}// compute suffix length at index iint[] suffix(char[] pattern) {int m = pattern.length;int[] suff = new int[m];suff[m - 1] = m;for (int i = m - 2; i >= 0; i--) {int j = i;// compute suffix length at index iwhile (j >= 0 && pattern[j] == pattern[m - 1 - (i - j)])j--;suff[i] = i - j;}return suff;}public static void main(String[] args) throws Exception {String haystack = "mahtavaatalomaisemaomalomailuun";String needle = "maoma";System.out.println(new Solution().strStr(haystack, needle));}}