var numbers=new List<int>(){1,1,1,1,1,2,2,1,2,3};
numbers.Sort();
var result=new Dictionary<int,int>();
for(int i=1;i<numbers.Count;i++)
{
if(numbers[i]==numbers[i-1]) {
if(!result.Keys.Contains(numbers[i]))
result.Add(numbers[i],1);
else result[numbers[i]]++;
}
}
foreach(var x in result.Keys)...