1. Given a string s, find the minimum number of substrings you can create without having the same letters repeating in each substring.
   E.g world -> 5, as the string has no letters that occur more than once.
   dddd -> 4, as you can only create substring of each character.
   abba -> 2, as you can make substrings of ab, ba.
   cycle-> 2, you can create substrings of (cy, cle) or (c, ycle)

Provide solution in PYTHON !!!!!