BronzeCrab

def task1(alist1, alist2):
    """Временная сложность o(len(alist1)) если len(alist1)>len(alist2)"""
    aset = set(alist2)
    out = [x for x in alist1 if x not in aset]
    return out

assert(task1([], [])) == []
assert(task1([1, 2, 3], [2, 4, 5])) == [1, 3]
assert(task1([1, 2, 3], [4, 5])) == [1, 2, 3]
assert(task1([1, 2, 3], [1, 2])) == [3]