Given an array of integers, return indices of the two numbers such that they add up to a specific target. You may assume that each input would have exactly one solution, and you may not use the same element twice. Example: Given nums  2, 7, 11, 15, target  9, Because nums0  nums1  2  7  9, return 0, 1
def two_sum(array, target):
    dic = {}
    for i, num in enumerate(array):
        if num in dic:
            return dic[num], i
        else:
            dic[target - num] = i
    return None
