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.

Approach

C++

#include <bits/stdc++.h>
using namespace std;

string largestOddNumber(string num)
{

    int n = num.size();

    int i = n - 1;
    while (i >= 0 && (num[i] == '0' || num[i] == '2' ||
           num[i] == '4' || num[i] == '6' || num[i] == '8'))
    {
        i--;
    }
    if (i < 0)
        return "";
    return num.substr(0, i + 1);
}

int main()
{
    string num = "52";

    cout << largestOddNumber(num) << "\n";

    return 0;
}