leetcode345

public class Solution {
    public string ReverseVowels(string s) {
        var str = s.ToList();
            var Vowels = new List<char>();

            for (int i = 0; i < str.Count; i++)
            {
                var c = str[i];
                if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u'
                    || c == 'A' || c == 'E' || c == 'I' || c == 'O' || c == 'U')
                {
                    Vowels.Add(c);
                }
            }
            if (Vowels.Count > 0)
            {
                Vowels.Reverse();
                int j = 0;
                for (int i = 0; i < str.Count; i++)
                {
                    var c = str[i];                    
                    if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u'
                    || c == 'A' || c == 'E' || c == 'I' || c == 'O' || c == 'U')
                    {
                        str[i] = Vowels[j];
                        j++;
                    }
                }
            }

            StringBuilder sb = new StringBuilder();
            foreach (var c in str)
            {
                sb.Append(c);
            }

            return sb.ToString();
    }
}

https://leetcode.com/problems/reverse-vowels-of-a-string/#/description