size_t goLeft(size_t a, size_t b, const string& pattern, const string& text,
              const SuffixArray& suffixArr, size_t prev) {
  if (a > b) return prev;
  size_t mid = (a + b)/2;
  if (!equalityCheck(pattern, text.substr(suffixArr[mid]))) {
    return goLeft(mid+1, b, pattern, text, suffixArr, prev);
  }
  return goLeft(0, mid-1, pattern, text, suffixArr, mid);
}

size_t goRight(size_t a, size_t b, const string& pattern, const string& text,
              const SuffixArray& suffixArr, size_t prev) {
  if (a > b) return prev;
  size_t mid = (a + b)/2;
  if (!equalityCheck(pattern, text.substr(suffixArr[mid]))) {
    return goRight(0, mid-1, pattern, text, suffixArr, prev);
  }
  return goRight(mid+1, b, pattern, text, suffixArr, mid);
}