【DP五十题】P1736 创意吃鱼法

const int N=2510;
int f[N][N];//记录以i,j为右下角（或左下角）能吸到的最多的鱼
int l[N][N];//记录最多能向左边扩展多少个0
int up[N][N];//记录最多能向上边扩展多少个0
int r[N][N];//记录最多能向右边扩展多少个0
int a[N][N];
int n,m,ans=INT_MIN;

int main(){
	#ifdef WIN32
	freopen("test.txt","r",stdin);
	#endif
	rd(n),rd(m);
	rep(i,1,n)
		rep(j,1,m){
			rd(a[i][j]);
		}
	rep(i,1,n){
		rep(j,1,m){
			if(a[i][j]==0){
				l[i][j]=l[i][j-1]+1;
				up[i][j]=up[i-1][j]+1;
			}
			else if(a[i][j]==1){
				f[i][j]=min(f[i-1][j-1],min(l[i][j-1],up[i-1][j]))+1;
			}
			ans=max(ans,f[i][j]);
		}
	}
	mem(f,0),mem(up,0);
	rep(i,1,n){
		dwn(j,m,1){
			if(a[i][j]==0){
				r[i][j]=r[i][j+1]+1;
				up[i][j]=up[i-1][j]+1;
			}
			else if(a[i][j]==1){
				f[i][j]=min(f[i-1][j+1],min(r[i][j+1],up[i-1][j]))+1;
			}
			ans=max(ans,f[i][j]);
		}
	}
	printf("%d",ans);
	return 0; 
}