c#如何判断字符串中相同字符串的个数 （相同字符在字符串中出现的次数）

 /// <summary>
        /// 计算字符串中子串出现的次数
        /// </summary>
        /// <param name="str">字符串</param>
        /// <param name="substring">子串</param>
        /// <returns>出现的次数</returns>
        static int SubstringCount(string str, string substring)
        {
            if (str.Contains(substring))
            {
                string strReplaced = str.Replace(substring, "");
                return (str.Length - strReplaced.Length) / substring.Length;
            }

            return 0;
        }

 string a = "abcdefababctrb";
            string b = "b";

            int c = SubstringCount(a, b);  //这里的c就是b在a中出现的次数了
            Console.Write(c);
            Console.ReadLine();