944 - Delete Columns to Make Sorted

944. Delete Columns to Make Sorted

Problem Statement

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.

 

Example 1:

Input: strs = ["cba","daf","ghi"]
Output: 1
Explanation: The grid looks as follows:
  cba
  daf
  ghi
Columns 0 and 2 are sorted, but column 1 is not, so you only need to delete 1 column.

Example 2:

Input: strs = ["a","b"]
Output: 0
Explanation: The grid looks as follows:
  a
  b
Column 0 is the only column and is sorted, so you will not delete any columns.

Example 3:

Input: strs = ["zyx","wvu","tsr"]
Output: 3
Explanation: The grid looks as follows:
  zyx
  wvu
  tsr
All 3 columns are not sorted, so you will delete all 3.

 

Constraints:

• n == strs.length
• 1 <= n <= 100
• 1 <= strs[i].length <= 1000
• strs[i] consists of lowercase English letters.

Solutions

Java

class Solution {
  public int minDeletionSize(String[] strs) {
    if (strs == null || strs.length == 0)
      return 0;

    int count = 0;

    for (int i = 0; i < strs[0].length(); i++) {
      char ch = strs[0].charAt(i);
      for (int j = 0; j < strs.length; j++) {
        char curr = strs[j].charAt(i);
        if (curr < ch) {
          count++;
          break;
        }
        ch = curr;
      }
    }

    return count;
  }
}

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