救救孩子吧！

#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int n,m,kkk,ans=1e8,f[1001][1001][10],f1[1000][1001][10],a[1001][1001];
int check(int xx1,int yy1,int xx2,int yy2)
{
	int k=log2(xx2-xx1+1);
	int ans1=max(f[xx1][yy1][k],f[xx2-(1<<k)+1][yy1][k]);
	int ans2=max(f[xx1][yy2-(1<<k)+1][k],f[xx2-(1<<k)+1][yy2-(1<<k)+1][k]);
	return max(ans2,ans1);
}
int check1(int xx1,int yy1,int xx2,int yy2)
{
	int k=log2(xx2-xx1+1);
	int ans1=min(f1[xx1][yy1][k],f1[xx2-(1<<k)+1][yy1][k]);
	int ans2=min(f1[xx1][yy2-(1<<k)+1][k],f1[xx2-(1<<k)+1][yy2-(1<<k)+1][k]);
	return min(ans2,ans1);
}
int main()
{
	cin>>n>>m>>kkk;
	for(int i=1; i<=n; i++)
	 for(int j=1; j<=m; j++)
	    scanf("%lld",&a[i][j]);
	for(int k=0; k<=log2(100); k++)
	 for(int i=1; i+(1<<k)-1<=n; i++)
	  for(int j=1; j+(1<<k)-1<=m; j++)
	    {
	    	if(k==0)
	    	 {
	    	   f[i][j][k]=a[i][j];
	    	   f1[i][j][k]=a[i][j];
			 }
	    	else
	    	 {
	    	   f[i][j][k]=max(f[i][j][k-1],f[i+(1<<(k-1))][j][k-1]);
	    	   f1[i][j][k]=min(f1[i][j][k-1],f1[i+(1<<(k-1))][j][k-1]);
	           f[i][j][k]=max(f[i][j][k-1],f[i][j+(1<<(k-1))][k-1]);
	           f1[i][j][k]=min(f1[i][j][k-1],f1[i][j+(1<<(k-1))][k-1]);
			 }
		}
    for(int i=1; i+kkk-1<=n; i++)
     for(int j=1; j+kkk-1<=m; j++)
        ans=min(ans,check(i,j,i+kkk-1,j+kkk-1)-check1(i,j,i+kkk-1,j+kkk-1));
	cout<<ans;
	return 0;
}