Get Min Cost Data

Problem Overview

• Replace all '?' in a lowercase string to minimize total cost, where an index’s cost equals the number of earlier indices with the same letter.
• Return the resulting string; if multiple reach the minimum cost, choose the lexicographically smallest; 1 ≤ |data| ≤ 1e5 and at least one '?'.
• Context: data interpolation model with 26 classifications (a–z).
• Source: Amazon interviews; a coding interview problem and common interview question.