Fastest way to Remove Duplicate Value from a list<> by lambda

Question

what is fastest way to remove duplicate values from a list. Assume List longs = new List { 1, 2, 3, 4, 3, 2, 5 }; So I am interesting in

Answer 1

A simple intuitive implementation

public static List RemoveDuplicates(List listPoints)
{
    List result = new List();

    for (int i = 0; i < listPoints.Count; i++)
    {
        if (!result.Contains(listPoints[i]))
            result.Add(listPoints[i]);
    }

    return result;
}