'''
You are given two integer arrays nums1 and nums2 of equal length n and an integer k. You can perform the following operation on nums1:

Choose two indexes i and j and increment nums1[i] by k and decrement nums1[j] by k. In other words, nums1[i] = nums1[i] + k and nums1[j] = nums1[j] - k.
nums1 is said to be equal to nums2 if for all indices i such that 0 <= i < n, nums1[i] == nums2[i].

Return the minimum number of operations required to make nums1 equal to nums2. If it is impossible to make them equal, return -1.



Example 1:

Input: nums1 = [4,3,1,4], nums2 = [1,3,7,1], k = 3
Output: 2
Explanation: In 2 operations, we can transform nums1 to nums2.
1st operation: i = 2, j = 0. After applying the operation, nums1 = [1,3,4,4].
2nd operation: i = 2, j = 3. After applying the operation, nums1 = [1,3,7,1].
One can prove that it is impossible to make arrays equal in fewer operations.
Example 2:

Input: nums1 = [3,8,5,2], nums2 = [2,4,1,6], k = 1
Output: -1
Explanation: It can be proved that it is impossible to make the two arrays equal.


Constraints:

n == nums1.length == nums2.length
2 <= n <= 105
0 <= nums1[i], nums2[j] <= 109
0 <= k <= 105
'''
import unittest

from typing import *

class Solution:
    def minOperations(self, nums1: List[int], nums2: List[int], k: int) -> int:
        if k == 0:
            return 0 if nums1 == nums2 else -1
        if sum(nums1) != sum(nums2):
            return -1
        res = 0
        for i in range(len(nums1)):
            dis = abs(nums1[i] - nums2[i])
            if dis % k != 0:
                return -1
            res += dis // k
        return res // 2


class TestSolution(unittest.TestCase):

    def test_case(self):
        examples = (
            (([4,3,1,4], [1,3,7,1], 3), 2),
        )
        for first, second in examples:
            self.assert_function(first, second)

    def assert_function(self, first, second):
        self.assertEqual(Solution().minOperations(*first), second,
                         msg="first: {}; second: {}".format(first, second))


unittest.main()
