代码

#include <cstdio>#include <iostream>#define N 2510#define max(x, y) ((x) > (y) ? (x) : (y))#define min(x, y) ((x) < (y) ? (x) : (y))int n, m, ans;unsigned short up[N][N], left[N][N], right[N][N], f[N][N][2];bool a[N][N];inline int read(){    int x = 0, f = 1;    char ch = getchar();    for(; !isdigit(ch); ch = getchar()) if(ch == ‘-‘) f = -1;    for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - ‘0‘;    return x * f;}int main(){	int i, j;	n = read();	m = read();	for(i = 1; i <= n; i++)		for(j = 1; j <= m; j++)		{			f[i][j][0] = f[i][j][1] = a[i][j] = read();			up[i][j] = a[i - 1][j] ? 0 : up[i - 1][j] + 1;			left[i][j] = a[i][j - 1] ? 0 : left[i][j - 1] + 1;		}	for(i = 1; i <= n; i++)		for(j = m; j >= 1; j--)			right[i][j] = a[i][j + 1] ? 0 : right[i][j + 1] + 1;	for(i = 1; i <= n; i++)		for(j = 1; j <= m; j++)		{			if(!a[i][j]) continue;			f[i][j][0] = min(f[i - 1][j - 1][0], min(up[i][j], left[i][j])) + 1;			f[i][j][1] = min(f[i - 1][j + 1][1], min(up[i][j], right[i][j])) + 1;			ans = max(ans, max(f[i][j][0], f[i][j][1]));		}	printf("%d\n", ans);	return 0;}