Leetcode 3114. Latest Time You Can Obtain After Replacing Characters

Given a "HH:MM" 12-hour time string with some digits replaced by '?', replace all '?' to form the latest valid time (hours 00–11, minutes 00–59). This is solved by making greedy, position-wise digit choices under the positional constraints (e.g., hour tens and ones bounds, minute tens ≤5).