class Solution {
    public List<String> cellsInRange(String s) {
        ArrayList<String> list = new ArrayList<>();
        StringBuilder sb = new StringBuilder();
        
        for(int i=(int)(s.charAt(0)); i<=(int)(s.charAt(3)); i++){
            for(int j=Integer.valueOf(s.charAt(1)-'0'); j<=Integer.valueOf(s.charAt(4)-'0'); j++){
                sb = new StringBuilder(""+(char)i);
                sb.append(j);
                list.add(sb.toString());
            }
        }
        
        return list;
    }
}