def char_without_duplicates(str_input): chars_list = [0]*256 for ch in str_input: chars_list[ord(ch)] += 1 char_index = 0 for i in str_input: if chars_list[ord(i)] == 1: return char_index char_index += 1 return -1 str_input = "abcabcffkabcabc" print "{} is a char without duplicates.".format(str_input[char_without_duplicates(str_input)])