public static String gridChallenge(List<String> grid) {
        final String YES = "YES";
        final String NO = "NO";
        int columnCount = grid.get(0).length();
        int rowCount = grid.size();
        
        var sortedRowsGrid = grid.stream()
            .map(row -> 
                row.chars().sorted().mapToObj(num -> (char) num).collect(toList())
            ).collect(toList());
        
        for (int j = 0; j < columnCount; j++) {
            for (int i = 1; i < rowCount; i++) {
                char currentLetter = sortedRowsGrid.get(i).get(j);
                char previousLetter = sortedRowsGrid.get(i - 1).get(j);
                
                if (currentLetter < previousLetter) {
                    return NO;
                }  
            } 
        }
        
        return YES;
    }