static string GetRepeatedElement(string[] strs, int repeats)
    {
        Dictionary<string, int> dict = new Dictionary<string, int>();
        foreach (string s in strs)
        {
            if (dict.ContainsKey(s)) dict[s]++;
            else dict[s] = 1;
        }

        foreach (string s in dict.Keys)
        {
            if (dict[s] == repeats) return s;
        }
        return null;
    }

------解决方案--------------------
C# code

private string[] bindGrid(string[] array,int i)
{
    HashTable ht = new HashTable();
    foreach(string s in array)
    {
        if(ht.ContainsKey(s))
            ht[s]=Convert.ToInt32(ht[s])+1;
        else
            ht.Add(s,1);
    }
    List<string> list=new List<string>();
    IDictionaryEnumerator ide = ht.GetEnumerator();
    while(ide.MoveNext())
    {
        if(ide.Value.ToString()==i)
            list.Add(ide.Value.ToString());
    }
    string[] result= list.ToArray();
    return result;
}

------解决方案--------------------
string[] asa = new string[] {"1","1","2","1","3","3","1","5","3","3","3","3","3" };  
           bindGrid(asa,5);  

private static void bindGrid(string[] n,int max)  
       {  
           int count=0;  
           for (int i = 0; i < n.Length;i++ )  
           {               
               for (int j = i + 1; j < n.Length;j++ )  
               {  
                   if (count-1 > max)  
                   {  
                       Console.Write(n[i].ToString());  
                       Console.Read();  
                   }  
                   else  
                   {  
                       if (n[i].Equals(n[j])) count++;  
                   }  
               }  
           }  
       }

------解决方案--------------------
C# code

        string[] str = new string[] { "a", "b", "a", "c", "d", "e", "c", "a" ,"e","a","c","c","c","a"};
        public System .Collections .ArrayList  bindGrid(string[] str, int i)
        {
            int counter=0;         
            System.Collections.ArrayList alist = new System.Collections.ArrayList();
            for (int j = 0; j < str.Length; j++)
            {
                counter = 0;
                for (int k = 0; k < str.Length; k++)
                {
                    if (str[j] == str[k])
                        counter++;
                }

                if (counter == i&& alist .IndexOf (str [j])<0)//滤除相同元素
                    alist.Add(str[j]);
                

            }
            return alist;           

        }

------解决方案--------------------
返回string[] 的话可参考5楼的方式.
return (string [])alist.ToArray(typeof(string));


------解决方案--------------------