Remove List Elements that appear more than Once In Place

Question

There is a similar question posted, but I do not have the rep to ask a follow-up question in that thread :(

That question and solution is HERE.

If I have a Lis

Answer 1

I have two options for you, one that uses HashSet and other Linq .

Option 1:

Using HashSet, loop through collection and insert if it not exist and remove if it exists.

HashSet hash = new HashSet();

foreach(var number in list)
{
    if(!hash.Contains(number)) hash.Add(number);
    else hash.Remove(number);               
}
list = hash.ToList();

Option 2:

Simple Linq, group the elements and filter whose count >1.

var list= list.GroupBy(g=>g)
    .Where(e=>e.Count()==1)
    .Select(g=>g.Key)
    .ToList();

There is big performance gain using HashSet over Linq, it is obvious, Linq(in this case) require multiple iterations, where as HashSet uses single iteration and provides LookUp (for adding/removing) with O(1) access.

Elapsed Time (Using Linq): 8808 Ticks
Elapsed Time (Using HashSet): 51 Ticks

Working Demo