原题链接：Problem - 289B - Codeforces

题意:给你一个n * m的矩阵和一个值d，对于每个数都可以进行无数次加d和减d的操作，问你最少操作次数是多少，能使矩阵每个数都一样。

AC代码： 

#include<bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define ios ios::sync_with_stdio(false);cin.tie(0); cout.tie(0);
typedef pair<int, int> PII;
const double pi = acos(-1.0);
#define rep(i, n) for (int i = 1; i <= (n); ++i)
#define rrep(i, n) for (int i = n; i >= (1); --i)
typedef long long ll;
#define sqar(x) ((x)*(x))

const int N = 110 * 110;
int a[N];
int main(){
  ll res = 0;
  int n, m, d;
  cin >> n >> m >> d;
  n *= m;
  rep(i, n) cin >> a[i];
  rep(i, n) if(a[i] % d != a[1] % d){
    cout << -1;
    return 0;
  }
  sort(a + 1, a + 1 + n);
  m = a[(n + 1) / 2];
  rep(i, n) res += abs(a[i] - m);
  cout << res / d;
  return 0;
}