codevs 1259 最大正方形子矩阵 WD

#include <cstdio>
#include <cstring>

#define ref(i,x,y)for(int i=x;i<=y;i++)
#define def(i,x,y)for(int i=x;i>=y;i--)
#define max(a,b)a=a>b?a:b;

int n,m,ans;
int a[1001][1001],f[1001][1001],s[2][1001][1001];

int main()
{
    scanf("%d%d",&n,&m);
    ref(i,1,n)ref(j,1,m)
        scanf("%d",&a[i][j]);
    ref(i,1,n)ref(j,1,m)
        if(!a[i][j])
        {
            s[1][i][j]=s[1][i][j-1]+1;
            s[0][i][j]=s[0][i-1][j]+1;
        }
    ref(i,1,n)ref(j,1,m)
        if(a[i][j])
        {
            int p=f[i-1][j-1];
            if(p<=s[1][i][j-1]&&p<=s[0][i-1][j])
                f[i][j]=f[i-1][j-1]+1;
            max(ans,f[i][j]);
        }
    memset(f,0,sizeof f);
    ref(i,1,n)def(j,m,1)
        if(a[i][j])
        {
            int p=f[i-1][j+1];
            if(p<=s[1][i][j+p]&&p<=s[0][i-1][j])
                f[i][j]=f[i-1][j+1]+1;
            max(ans,f[i][j]);
        }
    printf("%d",ans);
    return 0;
}