1903\. Largest Odd Number in String

Easy

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 an empty string_ `""` _if no odd integer exists_.

A **substring** is a contiguous sequence of characters within 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:** ""

**Explanation:** There are no odd numbers in "4206".

**Example 3:**

**Input:** num = "35427"

**Output:** "35427"

**Explanation:** "35427" is already an odd number.

**Constraints:**

*   <code>1 <= num.length <= 10<sup>5</sup></code>
*   `num` only consists of digits and does not contain any leading zeros.