This problem was recently asked by Google.

Given a list of numbers and a number k, return whether any two numbers from the list add up to k.

For example, given [10, 15, 3, 7] and k of 17, return true since 10 + 7 is 17.

Bonus: Can you do this in one pass?

Very Bad Solution:

def add_up_to_k_v1(mylist, k):

    ans = [x+y==k for x in mylist for y in mylist]

    return sum(ans) > 0

My Original Solution Demo

def add_up_to_k_v2(mylist, k):
    for i, num in enumerate(mylist):
        if k-num in mylist:
            return True
    return False


assert add_up_to_k_v1(mylist, k) == True, 'fail'
assert add_up_to_k_v2(mylist, k) == True, 'fail'

Zyaad Jaunoo: Using a “set” instead of a list will bring down the complexity to nlogn.