```cpp
#include<bits/stdc++.h>
using namespace std;
const int N=505;
int n,m,a[N][N],f[N][N][N];
int main(){
scanf("%d%d",&n,&m);
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++) scanf("%d",&a[i][j]);
f[1][1][1]=a[1][1];
for(int p=2;p<=n+m-1;p++)
for(int i=1;i<=n&&i<=p;i++)//是n捏
for(int j=1;j<=n&&j<=p;j++){
if(i==1&&j==1) continue;
f[p][i][j]=max(max(f[p-1][i][j],f[p-1][i-1][j]),max(f[p-1][i][j-1],f[p-1][i-1][j-1]));
if(i==j) f[p][i][j]+=a[i][p-i+1];
else f[p][i][j]+=a[i][p-i+1]+a[j][p-j+1];
}
printf("%d",f[n+m-1][n][n-1]);
return 0;
}//求个关注谢谢
```
@[lct201714](/user/372238)
by z_z_b_ @ 2024-04-12 19:03:00
@[z_z_b_](/user/956129) 已关谢谢
by lct201714 @ 2024-04-13 08:36:58