find pair of numbers in array that add to given sum

Question

Question: Given an unsorted array of positive integers, is it possible to find a pair of integers from that array that sum up to a given sum?

Constraints: This shou

Answer 1

def pair_sum(arr,k):
    counter = 0
    lookup = set()
    for num in arr:
        if k-num in lookup:
            counter+=1
        else:
            lookup.add(num)
    return counter
    pass
pair_sum([1,3,2,2],4)

The solution in python