Largest Odd Number

You are given a string num, representing a large integer. Return the largest-valued odd integer (as a string) that is a non-empty substring of num, or "null" if no odd integer exists.

A substring is a contiguous sequence of characters within a string.

Input Format

First Parameter: String num

Output Format

Return a string

Example 1

Input: num = "52"
Output: "5"
Explanation: The only non-empty substrings are "5", "2", and "52". "5" is the only odd number.

Example 2

Input: num = "4206"
Output: "null"
Explanation: There are no odd numbers in "4206".

Example 3

Input: num = "35427"
Output: "35427"
Explanation: "35427" is already an odd number.

Constraints

• 1 <= num.length <= 10^5
• num only consists of digits and does not contain any leading zeros.
• Expected Time Complexity - O(n)
• Expected Space Complexity - O(1)