Question

I’m having trouble coming up with the most efficient algorithm to remove duplicates from List<List<int>>, for example (I know this looks like a list of int[], but just doing it that way for visual purposes:

my_list[0]= {1, 2, 3};
my_list[1]= {1, 2, 3};
my_list[2]= {9, 10, 11};
my_list[3]= {1, 2, 3};

So the output would just be

new_list[0]= {1, 2, 3};
new_list[1]= {9, 10, 11};

Let me know if you have any ideas. I would really appreciate it.

Answer 1

Build custom of EqualityComparer<List<int>>:

public class CusComparer : IEqualityComparer<List<int>>
{
    public bool Equals(List<int> x, List<int> y)
    {
        return x.SequenceEqual(y);
    }

    public int GetHashCode(List<int> obj)
    {
        int hashCode = 0;

        for (var index = 0; index < obj.Count; index++)
        {
            hashCode ^= new {Index = index, Item = obj[index]}.GetHashCode();
        }

        return hashCode;
    }
}

Then you can get the result by using Distinct with custom comparer method:

var result = my_list.Distinct(new CusComparer());

Edit:

Include the index into method GetHashCode to make sure different orders will not be equal