Second Largest Digit in a String

Problem Statement

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.

Examples

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.

Algorithm

1. Extract all unique digits from the string.
2. If the count of unique digits is less than 2, return -1.
3. Convert the digits to integers and sort them in descending order.
4. Return the second largest digit.

Python Code

class Solution:
    def secondHighest(self, s: str) -> int:
        digits = {char for char in s if char.isdigit()}
        if len(digits) < 2:
            return -1
        sorted_digits = sorted(map(int, digits), reverse=True)
        return sorted_digits[1]

C++ Code

#include <string>
#include <set>
#include <algorithm>

class Solution {
public:
    int secondHighest(std::string s) {
        std::set<char> digits;
        for (char ch : s) {
            if (isdigit(ch)) {
                digits.insert(ch);
            }
        }
        if (digits.size() < 2) {
            return -1;
        }
        auto it = digits.rbegin();
        std::advance(it, 1);
        return *it - '0';
    }
};

Java Code

import java.util.Set;
import java.util.TreeSet;

class Solution {
    public int secondHighest(String s) {
        Set<Character> digits = new TreeSet<>();
        for (char ch : s.toCharArray()) {
            if (Character.isDigit(ch)) {
                digits.add(ch);
            }
        }
        if (digits.size() < 2) {
            return -1;
        }
        return Character.getNumericValue(((TreeSet<Character>) digits).lower(((TreeSet<Character>) digits).last()));
    }
}

JavaScript Code

/**
 * @param {string} s
 * @return {number}
 */
var secondHighest = function (s) {
  let digits = new Set();
  for (let char of s) {
    if (/\d/.test(char)) {
      digits.add(char);
    }
  }
  if (digits.size < 2) {
    return -1;
  }
  let sortedDigits = Array.from(digits)
    .map(Number)
    .sort((a, b) => b - a);
  return sortedDigits[1];
};