LeetCode 1796. Second Largest Digit in a String

Given an alphanumeric string s, return the second largest numerical digit that appears in s, or -1 if it does not exist.

An alphanumeric string is a string consisting of lowercase English letters and digits.

Example 1:

Input: s = "dfa12321afd"
Output: 2
Explanation: The digits that appear in s are [1, 2, 3]. The second largest digit is 2.

Example 2:

Input: s = "abc1111"
Output: -1
Explanation: The digits that appear in s are [1]. There is no second largest digit. 

Constraints:

• 1 <= s.length <= 500

• s consists of only lowercase English letters and/or digits.

Solution

class Solution {
public:
    int secondHighest(string s) {
        set<char> nums;
        for (char ch : s) {
            if (isdigit(ch)) {
                nums.insert(ch);
            }
        }
        
        if (nums.size() < 2) {
            return -1;
        }
        return *(++nums.rbegin()) - '0';
    }
};