字符串快速匹配算法sunday

public static int sundayMatch(String mainString, String pattenString) {
  if (mainString.length() < pattenString.length()) {
    return -1;
  }

  mainString = mainString.toLowerCase();
  pattenString = pattenString.toLowerCase();
  int mainIndex = 0;
  int pattenIndex = 0;

  while (mainIndex < mainString.length() && pattenIndex < pattenString.length()) {
    if (pattenString.charAt(pattenIndex) == mainString.charAt(mainIndex)) {
      pattenIndex++;
      mainIndex++;
    } else {
      mainIndex = mainIndex + pattenString.length() - pattenIndex;
      pattenIndex = 0;
      if (mainIndex < mainString.length()) {
        int index = pattenString.lastIndexOf(mainString.charAt(mainIndex));
        if (index == -1) {
          mainIndex = mainIndex + 1;
        } else {
          mainIndex = mainIndex - index;
        }
      } else {
        return -1;
      }
    }
  }
  return pattenIndex == pattenString.length() ? mainIndex - pattenString.length() : -1;
}