出个难题，哪位高人来解解决！！

Question

有个字符串 str=a,b,c,a,e,f,d,a,e,a
现在要统计出 这个字符串中 有多少个a,多少个b,多少个c

Answer 1

不会做,但有点思路,不知道对不对
做个循环把字符串中各个数字取一遍substring(i,i+1)
然后计数
case a  anum+=1
case b  bnum+=1
...代码不大会写,请指教.

Answer 2

/// <summary>
    /// 个数
    /// </summary>
    /// <param name="strText">字符串</param>
    /// <param name="strWord">单词：a,b,c,d,</param>
    /// <returns></returns>
public static int CountWord(string strText, string strWord)
    {
        int count = 0;
        if (!string.IsNullOrEmpty(strText))
        {
            string[] strWords = strText.Split(',');            for (int i = 0; i < strWords.Length; i++)
            {
                if (strWords [i] == strWord)         //是否相等
                {
                    count++;
                }
            }            
        }
        return count;     
    }

Answer 3

        private string GetSameCount(string str)
        {
            int length=str.Length;
            string result=string.Empty;
            if(length==0) return result;
            while(length>0)
            {
                string tempChar=str[0].ToString();
                string tempStr=str.Replace(tempChar,"");
                int tempLen=tempStr.Length;
                result+=(length-tempLen)+tempChar;
                length=tempLen;
            }
            return result;
        }调用时：
str="a,b,c,a,e,f,d,a,e,a";
string result=GetSameCount(str.Replace(",",""));

Answer 4

            string s="asdfasdf";
            Dictionary<char, int> list = new Dictionary<char, int>();
            foreach (char c in s.ToCharArray())
            {
                if (list.ContainsKey(c))
                {
                    list[c] += 1;
                }
                else
                {
                    list.Add(c, 1);
                }
            }

Answer 5

完整代码:
            string s="asdfasfdasedfdadfddddddf";
            Dictionary<char, int> list = new Dictionary<char, int>();
            foreach (char c in s.ToCharArray())
            {
                if (list.ContainsKey(c))
                {
                    list[c] += 1;
                }
                else
                {
                    list.Add(c, 1);
                }
            }
            foreach (KeyValuePair<char, int> item in list)
            {
                Console.WriteLine("字符{0}有{1}", item.Key, item.Value);
            }
            Console.Read();

Answer 6

建立一个数组count[26]，记录a-z的计数int[] count = new int[26];
for(int k = 0; k < str.Length; k++)
{
   if(char.IsLetter(str[k]))
   {
      int n = str[k] - 'A';
      if(n > 26) 
      {
         n = str[k] - 'a';
      }
      count[n]++;
    }
}