Minimum Operations to Make a Uni-Value Grid

/*
Logic:
The modulo of all elements with x must be same,otherwise you won't be able to make all elements
same.
push all elements in one grid,sort them and find the median.Then summation of absolute difference/x
will be the answer.
Answer on both median will be same in case of even number of elements in grid.
*/
int calculate_operations(vector <int> arr,int x,int mid){
    int ans=0;
    for(int i=0;i<arr.size();i++){
        if((mid-arr[i])%x!=0)return -1;
        ans+=abs((mid-arr[i])/x);
    }
    return ans;
}

class Solution {
public:
    int minOperations(vector<vector<int>>& grid, int x) {
        vector <int> arr;
        for(auto itr:grid){
            for(auto it:itr)
               arr.push_back(it);
        }
        if(arr.size()==1) return 0;
        sort(arr.begin(),arr.end());
        return calculate_operations(arr,x,arr[arr.size()/2]);
    }
};