Delete Columns to Make Sorted

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.

Code

Time Complexity: $O(N)$, Space Complexity: $O(1)$

class Solution {
public:
    int minDeletionSize(vector<string>& strs) {
        int count = 0;
        for(int i = 0; i < strs[0].size(); i++) {
            for(int j = 1; j < strs.size(); j++) {
                if(strs[j-1][i] > strs[j][i]) {
                    count++;
                    break;  
                }
            }
        }
        return count;
    }
};

Link

• Delete Columns to Make Sorted