2405. Optimal Partition of String 
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Problem
Given a string s, partition the string into one or more substrings such that the characters in each substring are unique. That is, no letter appears in a single substring more than once.
Return the minimum number of substrings in such a partition.
Note that each character should belong to exactly one substring in a partition.
Example 1:
Input: s = "abacaba"
Output: 4
Explanation:
Two possible partitions are ("a","ba","cab","a") and ("ab","a","ca","ba").
It can be shown that 4 is the minimum number of substrings needed.
Example 2:
Input: s = "ssssss"
Output: 6
Explanation:
The only valid partition is ("s","s","s","s","s","s").
Constraints:
1 <= s.length <= 105sconsists of only English lowercase letters.