gistfile1.txt

def find_sumpairs(n, numbers):
    # This assumes we can't count on the fact that the array will be sorted
    # So, sort it to make sure. Not that this could be skipped and save an O(n log n)
    best_case = sorted(numbers, reverse=True)
    if (n / 2) > best_case[0]:
        # if in a descending sorted array the left-most element
        # is less than a half the number we're looking for,
        # we can guarantee that the next number won't add up to n.
        # So skip here
        return False
    elif (best_case[0] + best_case[1]) == n:
        return True

    for i, sum1 in enumerate(best_case):
        for sum2 in best_case[i + 1:]:

            if sum2 < (n - sum1):
                break

            if sum1 + sum2 == n:
                return True

    return False


print find_sumpairs(12, [1, 2, 3, 4, 5, 6, 7])
print find_sumpairs(20, [8, 4, 3, 7, 10, 5, 9, 11])
print find_sumpairs(2, [1, 3, 2])
print find_sumpairs(6, [4, 5, 3])
print find_sumpairs(7, [4, 5, 3])