Leetcode 944. Delete Columns to Make Sorted

Problem

You are given an array of n strings strs, all of the same length.

The strings can be arranged such that there is one on each line, making a grid.

• For example, strs = "abc", "bce", "cae" can be arranged as follows:

  abc
  bce
  cae

You want to delete the columns that are not sorted lexicographically. In the above example (0-indexed), columns 0 ('a', 'b', 'c') and 2 ('c', 'e', 'e') are sorted, while column 1 ('b', 'c', 'a') is not, so you would delete column 1.

Return the number of columns that you will delete.

Algorithm

To count the number of columns not sorted in ascending order, a straightforward tally is ok.

Code

class Solution:
    def minDeletionSize(self, strs: List[str]) -> int:
        rows, cols, cnts = len(strs), len(strs[0]), 0
        for c in range(cols):
            for r in range(rows-1):
                if strs[r][c] > strs[r+1][c]:
                    cnts += 1
                    break
        return cnts