# LeetCode 1903. Largest Odd Number in String

## 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.

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 <= 105`
• `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).