public static String gridChallenge(List<String> grid){
        boolean isSorted = true;
        // sort and reinsert strings
        for(String str : grid){
            String sortedStr = sortedString(str);
            grid.set(grid.indexOf(str), sortedStr);
        }
        // check each char in the row < the char in the row below
        for(int col = 0; col < grid.get(0).length(); col++){
            for(int row = 0; row < grid.size() - 1; row++){
                if(grid.get(row).charAt(col) > grid.get(row + 1).charAt(col)) isSorted = false;
            }
        }

        return isSorted ? "YES" : "NO";
    }

    public static String sortedString(String s){
        char[] chars = s.toCharArray();
        Arrays.sort(chars);
        return new String(chars);
    }