static void Main(string[] args)
{
List<int> ids = new List<int>();
ids.Add(1);
ids.Add(2);
List<int> ids1 = new List<int>();
ids1.Add(1);
ids1.Add(2);
ids1.Add(3);
foreach (var i in ids1.Except(ids))
{
Console.Write(i);
}
foreach (var i in ids1.Intersect(ids))
{
Console.Write(i);
}
var c = ids.Cast<int>().Concat(ids1.Cast<int>()).GroupBy((t) => t).Where((t) => t.Count() == 1);
foreach (var d in c)
{
Console.Write(d.Key.ToString());
}