Replace dashes with nearest letter (tie-break by lexicographical order)

Problem: Replace '-' cells with the nearest letter (with tie-breaking) You are given an m x n character matrix grid. Each cell is either the dash character '-' or an English letter (e.g., 'a'-'z'; exact casing depends on the input). You must replace every '-' cell using letters from its Manhattan-distance-1 neighbors (4-directional adjacency: up, down, left, right; distance 1 means directly adjacent). If a '-' cell has one or more adjacent letters, replace it with any adjacent letter. Follow-up requirement: if there are multiple adjacent letters, you must replace it with the lexicographically smallest letter among them. You may return the resulting matrix or modify it in-place. Suggested I/O format Input: m n followed by m strings of length n. Output: m strings after replacement. Constraints (typical interview assumptions) 1 <= m, n <= 2000 Need near O(m*n) time. Example Input: 3 4 -a-- ---- --b- One valid output under the follow-up rule: aaaa abbb bbbb Example Input 1 1 a Output a