num contains the decimal digits of a large integer. Among all nonempty contiguous substrings representing odd integers, return the one with the greatest numeric value as a string. If none exists, return an empty string. The input may be too large for a fixed-width integer.
Example 1:
Input: num = "0"
Output: ""Explanation: The only nonempty substring is "0", which is even. No odd number can be selected.
Example 2:
Input: num = "1"
Output: "1"Explanation: The whole string represents the odd number 1.
Example 3:
Input: num = "2"
Output: ""Explanation: The only nonempty substring is "2", which is even, so the answer is an empty string.
Constraints:
1 <= num.length <= 100000- Only decimal digits occur, with no leading zeros.