You may exchange two decimal digits of the nonnegative integer num at most once. Return the largest integer obtainable. You may also leave the digits unchanged.
Example 1:
Input: num = 1993
Output: 9913Explanation: Swap the first digit with the rightmost 9 to obtain 9913. Using the other 9 would produce only 9193.
Example 2:
Input: num = 98368
Output: 98863Explanation: Swap the digit 3 with the final 8 to obtain 98863. The earlier 9 and 8 already form the largest possible prefix.
Example 3:
Input: num = 0
Output: 0Explanation: The only digit is 0, so there is no pair to swap and the result remains 0.
Constraints:
0 <= num <= 100000000