3803. Count Residue Prefixes

You are given a string s consisting only of lowercase English letters. A prefix of s is called a residue if the number of distinct characters in the prefix is equal to len(prefix) % 3. Return the count of residue prefixes in s. A prefix of a string is a non-empty substring that starts from the beginning of the string and extends to any point within it. Example 1: Input: s = "abc" Output: 2