## Description

https://leetcode.com/problems/largest-odd-number-in-string/

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:**

`1 <= num.length <= 10`

^{5}`num`

only consists of digits and does not contain any leading zeros.

## Explanation

Check the string from backwards, if find an odd character, that is the largest odd number.

## Python Solution

```
class Solution:
def largestOddNumber(self, num: str) -> str:
for i in range(len(num) - 1, -1, -1):
c = num[i]
if int(c) % 2 != 0:
return num[:i + 1]
return ""
```

- Time Complexity: O(N).
- Space Complexity: O(1).