看注释叭

看注释就可以了

#pragma GCC optimize(2)
#include <cstdio>
#define N 301
using namespace std;

inline int max(int a,int b) {return a > b ? a : b;} 
int f[N][N][N];   // 存储上半8字形矩形面积
int sum[N][N];    // 行前缀和，快速判断区间是否合法
int map[N][N];    // 存储地图
int n, ans, p;
char s[N];

int main()
{
   scanf("%d", &n);
   for (int i = 1;i <= n; ++i)
   {
   	scanf("%s", s + 1);
   	for (int j = 1;j <= n; ++j)
   		map[i][j] = s[j] == '*' ? 1 : 0,    // 缺陷记1，合法记0
   		sum[i][j] = sum[i][j - 1] + map[i][j];
   }

   // 预处理上半部分8字矩形面积
   for (int i = 1;i < n - 1; ++i)
   	for (int j = i + 2;j <= n; ++j)
   	{
   		p = 0;
   		for (int k = 1;k <= n; ++k)
   		{
   			if (map[k][i] || map[k][j]) p = 0;
   			if (sum[k][i - 1] == sum[k][j]) 
   				!p ? p = k : f[k][i][j] = (k - p - 1) * (j - i - 1);
   		}
   	}

   // DP优化，继承最大面积
   for (int k = 1;k <= n; ++k)
   {
   	for (int j = n;j > 3; --j)
   		for (int i = j - 3;i >= 0; --i) 
   			if (sum[k][i - 1] == sum[k][j]) f[k][i][j] = max(f[k][i][j], f[k][i + 1][j]);
   	for (int i = 1;i < n - 1; ++i)
   		for (int j = i + 3;j <= n; ++j) 
   			if (sum[k][i - 1] == sum[k][j]) f[k][i][j] = max(f[k][i][j], f[k][i][j - 1]);
   }

   // 计算下半部分，统计答案
   for (int i = 1;i < n - 1; ++i)
   	for (int j = i + 2;j <= n; ++j) 
   	{
   		p = 0;
   		for (int k = n;k; --k) 
   		{
   			if (map[k][i] || map[k][j]) p = 0;
   			if (sum[k][i - 1] == sum[k][j]) (!p) ? p = k : ans = max(ans, f[k][i][j] * (p - k - 1) * (j - i - 1));
   		}
   	}

   if (!ans) printf("-1");
   else printf("%d", ans);
   return 0;
}