51nod 1217 Minimum Modular

#include<bits/stdc++.h>
using namespace std;

void read(int&a){
    char ch;while(!((ch=getchar())>='0')&&(ch<='9'));
    a=ch-'0';while(((ch=getchar())>='0')&&(ch<='9'))a*=10,a+=ch-'0';
}

const int MAXN=1000100;
int a[MAXN],b[MAXN],dif[MAXN];

int main()
{
	int n,k,i,j,m,cnt_max,cnt,ct;
	while(~scanf("%d%d",&n,&k))
	{
		for(i=1;i<=n;i++)
			read(a[i]);
		sort(a+1,a+n+1);
		memset(dif,0,sizeof(dif));
		memset(b,0,sizeof(b));
		for(i=1;i<=n;i++)
			for(j=i+1;j<=n;j++)
				dif[a[j]-a[i]]++;
		m=n-k-1;
		cnt_max=k*(k+1)/2;
		while(m++)
		{
			cnt=ct=0;
			for(i=m;i<MAXN;i+=m)
				cnt+=dif[i];
			if(cnt>cnt_max)
				continue;
			for(i=1;i<=n;i++)
			{
				if(b[a[i]%m]==m)
				{
					ct++;
					if(ct>k)
						break;
				}
				b[a[i]%m]=m;
			} 
			if(ct<=k)
				break;
		}
		printf("%d\n",m);
	}
}