传纸条

#include<bits/stdc++.h>
using namespace std;
//和方格取数一样，一来一回可以看成走两次
int a[51][51],m,n,dp[51][51][51][51]={0};
int main() {
    cin>>m>>n;
    for(int i=1;i<=m;i++)
    for(int j=1;j<=n;j++) cin>>a[i][j];

for( int x1 = 1; x1 <= m; x1++ ) {
    for( int y1 = 1; y1 <= n; y1++ ) {
        for( int x2 = 1; x2 <= m; x2++ ) {
            for( int y2 = 1; y2 <= n; y2++ ){
                int t=max(dp[x1-1][y1][x2-1][y2],dp[x1][y1-1][x2][y2-1]);
                t=max(t,dp[x1-1][y1][x2][y2-1]);
                t=max(t,dp[x1][y1-1][x2-1][y2]);
                if(x1==x2&&y1==y2) dp[x1][y1][x2][y2]=t+a[x1][y1];
                else dp[x1][y1][x2][y2]=t+a[x1][y1]+a[x2][y2];
            }
        }
    }
}
    cout<<dp[m][n][m][n]<<endl;
    return 0;
}