2540. Minimum Common Value

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.

class Solution {
public:
    long long minOperations(vector<int>& nums1, vector<int>& nums2, int k) {
        long long plus = 0, minus = 0;
        if(k == 0) {
            for(int i = 0; i < nums1.size(); i++) {
                if(nums1[i] != nums2[i]) return -1;
            }
            return 0;
        }
        for(int i = 0; i < nums1.size(); i++) {
            if(nums1[i] == nums2[i]) continue;
            long long diff = nums1[i] - nums2[i];
            if(diff % k) return -1;
            if(diff > 0) plus += diff / k;
            else minus += -diff / k;
        }
        if(plus == minus) return plus;
        return -1;
    }
};