Given a positive integer num, split it into two non-negative integers num1 and num2 such that:
- The concatenation of num1 and num2 is a permutation of num.
- In other words, the sum of the number of occurrences of each digit in num1 and num2 is equal to the number of occurrences of that digit in num.
- num1 and num2 can contain leading zeros.
Return the minimum possible sum of num1 and num2.
Notes:
- It is guaranteed that num does not contain any leading zeros.
- The order of occurrence of the digits in num1 and num2 may differ from the order of occurrence of num.