func isIsomorphic(s string, t string) bool {
	if len(s) != len(t) {
		return false
	}
	var charMapS, charMapT [128]byte

	for i := range s {
		charS, charT := s[i], t[i]
		if (charMapS[charS] != 0 && charMapS[charS] != charT) ||
			(charMapT[charT] != 0 && charMapT[charT] != charS) {
			return false
		} else {
			charMapS[charS], charMapT[charT] = charT, charS
		}
	}

	return true
}