题解

#include <iostream>
using namespace std;

const int N = 20;
int a[N][N];
int dp[N][N][N];

int main()
{
    int n;
    cin >> n;
    
    int x,y,z;
    while(cin >> x >> y >> z)
    {
        if (x == 0 && y == 0 && z == 0) break;
        a[x][y] = z;
    }
    
    for (int i = 1;i <= 2 * n - 1;i++)
        for (int j = 1;j <= i;j++)
            for (int k = j;k <= i;k++)
            {
                dp[i][j][k] = max(max(dp[i - 1][j][k],dp[i - 1][j - 1][k - 1]),max(dp[i - 1][j - 1][k],dp[i - 1][j][k - 1]));
                dp[i][j][k] += a[i + 1 - j][j];
                if (j != k) dp[i][j][k] += a[i + 1 - k][k];
            }
            
    cout << dp[2 * n - 1][n][n] << endl;
    return 0;
}