Leetcode 3081. Replace Question Marks in String to Minimize Its Value

Given a string s with '?' wildcards, replace each '?' by a lowercase letter to minimize the total "value" — defined as the sum over positions of how many identical characters appeared before that position (i.e., penalizing repeated earlier occurrences). If multiple completions achieve the minimum value, return the lexicographically smallest one; n ≤ 1e5.