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();

		// pretreatment
		int[] bmBc = preBmBc(parr);
		int[] bmGs = preBmGs(parr);

		// find
		int i, j = 0;
		while (j <= slen - plen) {
			for (i = plen - 1; i >= 0 && parr[i] == sarr[i + j]; i--)
				;
			if (i < 0) { // find
				return j;
			} else {
				j += Math.max(bmBc[sarr[i + j]] - (plen - 1 - i), bmGs[i]);
			}
		}
		return -1;
	}

	// bad char heuristic
	int[] 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 heuristic
	int[] preBmGs(char[] pattern) {
		int m = pattern.length;
		int[] bmGs = new int[m];
		int[] suff = suffix(pattern);


		// case 3: not match
		for (int i = 0; i < m; i++) {
			bmGs[i] = m;
		}

		// case 2: partial match suffix
		int 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 suffix
		for (int i = 0; i <= m - 2; i++) {
			bmGs[m - 1 - suff[i]] = m - 1 - i;
		}
		return bmGs;
	}


	// compute suffix length at index i
	int[] 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 i
			while (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));
	}
}