题目

代码（还是我的好理解，(●'◡'●)）

#include <bits/stdc++.h>
using namespace std;
const int N = 55;
int w[N][N];
int f[2*N][N][N];
int main()
{
    int m, n;
    cin >> m >> n;
    
    for(int i = 1; i <= m; i++)
    {
        for(int j = 1; j <= n; j++)
        {
            cin >> w[i][j];
        }
    }
    for(int k = 2; k <= m+n; k++)
    {
        for(int i1 = 1; i1 <= m; i1++)
        {
            for(int i2 = 1; i2 <= m; i2++)
            {
                int j1 = k-i1;
                int j2 = k-i2;
                
                if(i1 == i2)
                {
                    if(i1 == 1 && j1 == 1);
                    else if(i1 == m && j1 == n);
                    else continue;
                }
                
                if(j1 >= 1 && j1 <= n && j2 >= 1 && j2 <= n)
                {
                    int &x = f[k][i1][i2];
                    int t = w[i1][j1] + w[i2][j2];
                    x = max(x, f[k-1][i1-1][i2-1] + t);
                    x = max(x, f[k-1][i1-1][i2] + t);
                    x = max(x, f[k-1][i1][i2-1] + t);
                    x = max(x, f[k-1][i1][i2] + t);
                }
            }
        }
    }
    
    cout << f[m+n][m][m];
}