Codeforces 838A - Binary Blocks(二维前缀和+容斥)

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define mem(a,b) memset((a),(b),sizeof(a))
const int INF=0x3f3f3f3f;
const int N=5000;
char mp[N][N];
int Mp[N][N]={0};

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n,m;
    cin>>n>>m;
    for(int i=1;i<=n;i++)cin>>mp[i]+1;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        Mp[i][j]=mp[i][j]-‘0‘;
    }
    for(int i=1;i<N;i++)
    {
        for(int j=1;j<N;j++)
        {
            Mp[i][j]+=Mp[i-1][j]+Mp[i][j-1]-Mp[i-1][j-1];
        }
    }
    int minn=min(n,m);
    int ans=INF;
    
    for(int i=2;i<=minn;i++)
    {
        bool flag=true;
        int x=n/i;
        int y=m/i;
        if(n%i)x++;
        if(m%i)y++;
        int cnt=0;
        for(int j=1;j<=x;j++)
        {
            for(int k=1;k<=y;k++)
            {
                if(j==1&&k==1)
                {
                    int t=Mp[j*i][k*i];
                    cnt+=min(i*i-t,t);
                }
                else
                {
                    int t=Mp[j*i][k*i]+Mp[j*i-i][k*i-i]-Mp[j*i][k*i-i]-Mp[j*i-i][k*i];
                    cnt+=min(i*i-t,t);
                }
            }
        }
        ans=min(ans,cnt);
    }
    printf("%d\n",ans);
    return 0;
}