C# 3.0: Need to return duplicates from a List<>

Question

I have a List<> of objects in C# and I need a way to return those objects that are considered duplicates within the list. I do not need the Distinct resultset, I need a

Answer 1

Create a new Dictionary foundColors and a List carsToDelete

Then you iterate through your original list of cars like so:

foreach(Car c in listOfCars)
{
    if (foundColors.containsKey(c.Color))
    {
        carsToDelete.Add(c);
    }
    else
    {
        foundColors.Add(c.Color, c);
    }
}

Then you can delete every car that's in foundColors.

You could get a minor performance boost by putting your "delete record" logic in the if statement instead of creating a new list, but the way you worded the question suggested that you needed to collect them in a List.