1，计算kmp失败回退函数：

   public static int[] getKmpFail(String pattern) {if (!hasLength(pattern)) throw new IllegalArgumentException("null or empty pattern is not allowed to get kmp fail array.");int i, j, len = pattern.length();int[] fail = new int[len];fail[0] = -1;for (j = 1; j < len; j++) {i = fail[j - 1];while ((pattern.charAt(j) != pattern.charAt(i + 1)) && (i >= 0)) {i = fail[i];}if (pattern.charAt(j) == pattern.charAt(i + 1)) {fail[j] = i + 1;} else {fail[j] = -1;}}return fail;}

２，查找子串：

    public static int kmpIndexOf(String source, String pattern, int from, int[] fail, int to) {int i = from, j = 0, lenp = pattern.length();while ((i < to) && (j < lenp)) {if (source.charAt(i) == pattern.charAt(j)) {i++;j++;} else {if (j == 0) {i++;} else {j = fail[j - 1] + 1;}}}return (j == lenp) ? (i - lenp) : -1;}

3，kmp多字符串查找：

    public static int[] kmpFirstMatch(String source, String[] patterns, int from, int[][] fails) {int[] indices = { -1, -1 };int to = source.length();for (int i = 0; i < patterns.length; i++) {//多次遍历source查找patterns[i]if(to - from < patterns[i].length()) continue;int index = kmpIndexOf(source, patterns[i], from, fails[i], to);if (index != -1 && (index < indices[0] || indices[0] == -1)) {indices[0] = to = index;//缩小范围，to之后的不用查找了indices[1] = patterns[i].length();//返回目标索引和长度to++;//if(from == index) break;上面的continue更优化}}return indices;}

4，step多字符串查找：

 public static int[] stepFirstMatch(char[] sources, int from, char[][] chars) {int[] indices = { -1, -1 };for (int i = from; i < sources.length; i++) {//从头至尾依次查找for (int j = 0; j < chars.length; j++) {if (sources[i] == chars[j][0]) {int k = 1;while (k < chars[j].length && i + k < sources.length && sources[i + k] == chars[j][k])k++;if (k == chars[j].length) {indices[0] = i;indices[1] = k;return indices;//找到就立即返回}}}}return indices;}

step比kmp方式要快一点，大概是基本类型上占些优势。

找到stepFirstMatch的一个合适用法：生成随机充值码时排出相似字符串！

//检查相似字符不能同时出现，生成的随机码串调用checkNoSimilarPairs(randomString)即可。private static String[] similarPairsString = {"0O", "1I", "2Z", "VY"};private static char[][] similarPairs = null;static {similarPairs = new char[similarPairsString.length*2][];for(int i = 0; i < similarPairsString.length; i++) {similarPairs[2*i] = similarPairsString[i].toCharArray();similarPairs[2*i + 1] = new StringBuilder(similarPairsString[i]).reverse().toString().toCharArray();}}private boolean checkNoSimilarPairs(String source) {return stepFirstMatch(source.toCharArray(), 0, similarPairs)[0] == -1;}