LeetCode-CSharp/Solution/1796.Second-largest-digit-in-a-string/1796-Second-largest-digit-in-a-string.cs at main · FakeStandard/LeetCode-CSharp · GitHub

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Solution._1796.Second_largest_digit_in_a_string
{
    public class _1796_Second_largest_digit_in_a_string
    {
        /// <summary>
        /// HashSet Solution
        /// </summary>
        /// <param name="s"></param>
        /// <returns></returns>
        public int SecondHighest(string s)
        {
            HashSet<int> set = new HashSet<int>();

            for (int i = 0; i < s.Length; i++)
            {
                if (s[i] >= '0' && s[i] <= '9')
                    set.Add(s[i] - '0');
            }

            if (set.Count <= 1) return -1;

            set.Remove(set.Max());

            return set.Max();
        }

        /// <summary>
        /// Iteration & HashSet
        /// </summary>
        /// <param name="s"></param>
        /// <returns></returns>
        //public int SecondHighest(string s)
        //{
        //    HashSet<int> set = new HashSet<int>();

        //    for (int i = 0; i < s.Length; i++)
        //    {
        //        if (s[i] >= '0' && s[i] <= '9')
        //            set.Add(s[i] - '0');
        //    }

        //    if (set.Count <= 1) return -1;

        //    int first = 0;
        //    int second = 0;

        //    foreach (var item in set)
        //    {
        //        if (item > first)
        //        {
        //            second = first;
        //            first = item;
        //        }
        //        else if (item < first && item > second)
        //            second = item;
        //    }

        //    return second;
        //}

        /// <summary>
        /// Iteration Solution
        /// </summary>
        /// <param name="s"></param>
        /// <returns></returns>
        //public int SecondHighest(string s)
        //{
        //    int first = -1;
        //    int second = -1;

        //    for (int i = 0; i < s.Length; i++)
        //    {
        //        if (char.IsDigit(s[i]) && s[i] - '0' > first)
        //        {
        //            second = first;
        //            first = s[i] - '0';
        //        }
        //        else if (char.IsDigit(s[i]) && s[i] - '0' > second && s[i] - '0' < first)
        //            second = s[i] - '0';
        //    }

        //    return second;
        //}
    }
}