Leetcode 1736. Latest Time by Replacing Hidden Digits

Given a time string "hh:mm" with some digits replaced by '?', replace each '?' to form the latest possible valid 24-hour time (00:00–23:59). The challenge is choosing the largest digit for each position under positional constraints (hour tens ≤2, minute tens ≤5, and if hour tens is 2 then hour units ≤3).