C++ 代码

#include <iostream>
#include <algorithm>
using namespace std;

const int N = 55;

int g[N][N];
int dp[N+N][N][N];

int n, m;

int main(){
    cin >> n >> m;
    for(int i = 1;i <= n;++i)
        for(int j = 1;j <= m;++j)
            cin >> g[i][j];

    for(int k = 2;k <= n + m;++k)   
        for(int i1 = 1;i1 <= n;++i1)
            for(int i2 = 1;i2 <= n;++i2){
                int j1 = k - i1, j2 = k - i2; 
                if(j1 >= 1 && j1 <= m && j2 >= 1 && j2 <= m){
                    int w = (i1 == i2 ? g[i1][j1] : g[i1][j1] + g[i2][j2]);
                    int &t = dp[k][i1][i2];
                    t = max(t, dp[k-1][i1][i2] + w);
                    t = max(t, dp[k-1][i1-1][i2] + w);
                    t = max(t, dp[k-1][i1][i2-1] + w);
                    t = max(t, dp[k-1][i1-1][i2-1] + w);
                }
            }
    cout << dp[n+m][n][n] << endl;    
    return 0;
}