public static String gridChallenge(List<String> grid) {
        if(grid.size() == 1) return "YES"; //no cols to check
        
        // 1. sort rows alphabetically ascending
        List<String> sortedGrid = new ArrayList<>();
        for(String row : grid){
            char[] chars = row.toCharArray();
            Arrays.sort(chars);
            sortedGrid.add(new String(chars));
        }
        
        // 2. check cols for alphabetically ascending order from top to bottom
        for(int col = 0; col < grid.get(0).length(); col++){
            for(int row = 1; row < grid.size(); row++){
                String currRow = sortedGrid.get(row);
                String prevRow = sortedGrid.get(row - 1);
                //check if col is in order
                if(currRow.charAt(col) < prevRow.charAt(col)) return "NO";
            }
        }
        return "YES";
    }