2033. Minimum Operations to Make a Uni-Value Grid

You are given a 2D integer grid of size m x n and an integer x. In one operation, you can add x to or subtract x from any element in the grid.

A uni-value grid is a grid where all the elements of it are equal.

Return the minimum number of operations to make the grid uni-value. If it is not possible, return -1.

class Solution {
public:
    int minOperations(vector<vector<int>>& A, int x) {
        vector<int> B;
        int res = 0;
        for(auto& row : A) for(auto& col : row) B.push_back(col);
        sort(begin(B), end(B));
        int median = B[B.size() / 2];
        for(auto& b : B) {
            int diff = abs(b-median);
            if(diff % x) return -1;
            res += diff / x;
        }
        return res;
    }
};