就对了最后一个点QAQ

#include <iostream>
using namespace std;
int n,x,y,s,a[55][55],f[55][55][55][55];
int main(){
	cin>>n;
	while (cin>>x>>y>>s&&x){
		a[x][y]=s;
	}
	for (int i=1;i<=n;i++){
		for (int j=1;j<=n;j++){
			for (int l=1;l<=n;l++){
				for (int k=1;k<=n;k++){
					f[i][j][k][l]=max(max(f[i-1][j][l-1][k],f[i][j-1][l][k-1]),max(f[i-1][j][l][k-1],f[i][j-1][l-1][k]))+a[i][j];
					if(i!=1&&j!=k) f[i][j][l][k]+=a[l][k];
				}
			}
		}
	}
	cout<<f[n][n][n][n];
	return 0;
}

蒟蒻必关，现等，急