Delete Columns to Make Sorted

main.md

Question

Approach

I iterate column by column. For each column, I compare characters from top to bottom. If I find any row where the character is smaller than the one above it, the column is not lexicographically sorted, so I count it as a deletion and move to the next column.

Implementation

class Solution:
    def minDeletionSize(self, strs: List[str]) -> int:
        rows, cols = len(strs), len(strs[0])
        deletions = 0

        for c in range(cols):
            for r in range(1, rows):
                if strs[r][c] < strs[r - 1][c]:
                    deletions += 1
                    break

        return deletions

Complexities

• Time: O(n × m)
• Space: O(1)

This solution works only because it blindly relies on problem constraints. It makes unchecked assumptions about non-empty input and equal-length strings, offers no defensive handling, and adds nothing beyond the most obvious brute-force approach. The explanation is minimal and lacks any justification beyond restating the code.

Yes, it's a brute force solution