01-02 Array pair sum

Array Pair Sum

Problem

Given an integer array, output all the unique pairs that sum up to a specific value k.

So the input:

pair_sum([1,3,2,2],4)

would return 2 pairs:

 (1,3)
 (2,2)

NOTE: FOR TESTING PURPOSES CHANGE YOUR FUNCTION SO IT OUTPUTS THE NUMBER OF PAIRS

Code

Create your solution in the form:

def pair_sum(arr: List, k: int) -> int:
    pass

Examples

>>> pair_sum([1,3,2,2],4)
2