Kata

Given a list of integers values, your job is to return the sum of the values; however, if the same integer value appears multiple times in the list, you can only count it once in your sum.

For example:

[ 1, 2, 3] ==> 6

[ 1, 3, 8, 1, 8] ==> 12

[ -1, -1, 5, 2, -7] ==> -1

[] ==> None

[ 1, 2, 3] ==> 6

[ 1, 3, 8, 1, 8] ==> 12

[ -1, -1, 5, 2, -7] ==> -1

[] ==> None

[ 1, 2, 3] ==> 6

[ 1, 3, 8, 1, 8] ==> 12

[ -1, -1, 5, 2, -7] ==> -1

[] ==> None

[ 1, 2, 3] ==> 6

[ 1, 3, 8, 1, 8] ==> 12

[ -1, -1, 5, 2, -7] ==> -1

[] ==> null

Kata.UniqueSum(new List<int> {1, 2, 3}) => 6

Kata.UniqueSum(new List<int> {1, 3, 8, 1, 8}) => 12

Kata.UniqueSum(new List<int> {-1, -1, 5, 2, -7}) => -1

Kata.UniqueSum(new List<int>()) => null

Good Luck!