delete_columns_to_make_sorted.dart

/*



-* 944. 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:

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.

*/

import 'dart:collection';

class A {
  int minDeletionSize(List<String> strs) {
    int answer = 0;
    for (int i = 0; i < strs[0].length; i++) {
      for (int j = 0; j < strs.length - 1; j++) {
        if (strs[j + 1].codeUnitAt(i) < strs[j].codeUnitAt(i)) {
          answer++;
          break;
        }
      }
    }
    return answer;
  }
}

class B {
  // O(n*m)
  int minDeletionSize(List<String> strs) {
    int deleted = 0;
    if (strs.length == 0) return deleted;
    int rowSize = strs[0].length;

    for (int col = 0; col < rowSize; col++) {
      if (!isSorted(strs, col)) deleted++;
    }

    return deleted;
  }

  bool isSorted(List<String> strs, int col) {
    int N = strs.length;
    int prev = 0;
    for (int i = 0; i < N; i++) {
      int c = strs[i].codeUnitAt(col);
      //If out of order
      if (c < prev) return false;
      //update prev
      prev = c;
    }

    return true; //In order the whole time
  }
}

class C {
  int minDeletionSize(List<String> strs) {
    HashSet<int> hashSET = HashSet();
    for (int j = 0; j < strs[0].length; j++) hashSET.add(j);
    for (int i = 1; i < strs.length; i++) {
      HashSet<int> tmp = HashSet();
      tmp.addAll(hashSET);
      for (int k in hashSET)
        if (strs[i].codeUnitAt(k) < strs[i - 1].codeUnitAt(k)) tmp.remove(k);
      hashSET = tmp;
    }
    return strs[0].length - hashSET.length;
  }
}