I stucked in the below question, specially they specify not using any data structure or convertion way.
/**

• Given an integer, sort the digits in ascending order and return the new integer.
• Ignore leading zeros.
• Parameters
• Input: num {Integer}
• Output: {Integer}
• Constraints
• Do not convert the integer into a string or other data type.
• Time: O(N) where N is the number of digits.
• Space: O(1)
• Examples
• 8970 --> 789
• 32445 --> 23445
• 10101 --> 111
  */

   public static int sortDigits(int n) {
     
    return -1;
   }