Subset sum recursively in Python

Question

I will be happy to get some help.

I have the following problem:

I\'m given a list of numbers seq and a target number and I need to write 2 thing

Answer 1

This is how I'd write the subset_sum:

def subset_sum(seq, target):
    if target == 0:
        return True

    for i in range(len(seq)):
        if subset_sum(seq[:i] + seq[i+1:], target - seq[i]):
            return True
    return False

It worked on a couple of examples:

>>> subset_sum([-1,1,5,4], 0))
True
>>> subset_sum([-1,1,5,4], 10)
True
>>> subset_sum([-1,1,5,4], 4)
True
>>> subset_sum([-1,1,5,4], -3)
False
>>> subset_sum([-1,1,5,4], -4)
False

To be honest I wouldn't know how to memoize it.

Old Edit: I removed the solution with any() because after some tests I found out that to be slower!

Update: Just out of curiosity you could also use itertools.combinations:

from itertools import combinations

def com_subset_sum(seq, target):
    if target == 0 or target in seq:
        return True

    for r in range(2, len(seq)):
        for subset in combinations(seq, r):
            if sum(subset) == target:
                return True
    return False

This can do better that the dynamic programming approach in some cases but in others it will hang (it's anyway better then the recursive approach).