<p>You are given two arrays <code>nums1</code> and <code>nums2</code> consisting of positive integers.</p>

<p>You have to replace <strong>all</strong> the <code>0</code>&#39;s in both arrays with <strong>strictly</strong> positive integers such that the sum of elements of both arrays becomes <strong>equal</strong>.</p>

<p>Return <em>the <strong>minimum</strong> equal sum you can obtain, or </em><code>-1</code><em> if it is impossible</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums1 = [3,2,0,1,0], nums2 = [6,5,0]
<strong>Output:</strong> 12
<strong>Explanation:</strong> We can replace 0&#39;s in the following way:
- Replace the two 0&#39;s in nums1 with the values 2 and 4. The resulting array is nums1 = [3,2,2,1,4].
- Replace the 0 in nums2 with the value 1. The resulting array is nums2 = [6,5,1].
Both arrays have an equal sum of 12. It can be shown that it is the minimum sum we can obtain.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums1 = [2,0,2,0], nums2 = [1,4]
<strong>Output:</strong> -1
<strong>Explanation:</strong> It is impossible to make the sum of both arrays equal.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums1.length, nums2.length &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= nums1[i], nums2[i] &lt;= 10<sup>6</sup></code></li>
</ul>

class Solution:
    def minSum(self, nums1: List[int], nums2: List[int]) -> int:

        def countNumZeros(arr):
            count = 0
            for x in arr:
                if x == 0:
                    count += 1
            return count

        # compute sums and count of zeros for each array
        sum1 = sum(nums1)
        sum2 = sum(nums2)

        zero_count1 = countNumZeros(nums1)
        zero_count2 = countNumZeros(nums2)

        # then split on the following cases

        # if both zero_counts zero, 
        # then only possible if same sum
        if zero_count1 == 0 and zero_count2 == 0:
            if sum1 == sum2:
                return sum1
            else:
                return -1

        # exactly one of arrays has 0 zeros
        if zero_count1 == 0 or zero_count2 == 0:
            # swap order for simplicity
            if zero_count2 == 0:
                nums1, nums2 = nums2, nums1
                sum1, sum2 = sum2, sum1
                zero_count1, zero_count2 = zero_count2, zero_count1

            # nums1 has zero 0s
            # only possible if sum nums1 >= min poss. nums2 sum
            min_sum_nums2 = sum2 + zero_count2
            if min_sum_nums2 > sum1:
                return -1
            else:
                return sum1
        
        # both arrays have zeros, always possible
        # take largest minimum possible sums of two
        min_sum_nums1 = sum1 + zero_count1
        min_sum_nums2 = sum2 + zero_count2
        return max(min_sum_nums1, min_sum_nums2)
        
       
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