Twin robots

#include <iostream>
#include <cstdio>
#include <climits>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <cstring>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <algorithm>
#include <sstream>
using namespace std;

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<vii> vvii;
typedef vector<bool> vb;

#define sz(c) int((c).size())
#define all(c) (c).begin(), (c).end()

vvi grid;
vector< vector< vector< vector<int> > > > memo;
int n, x;

int sum(int i, int j, int k, int l,vector< vector< vector< vector<int> > > >& memo)
{
    if(memo[i][j][k][l] != INT_MIN)
        return memo[i][j][k][l];

    else
    {
        int ans = grid[i][j] + grid[k][l], max = INT_MIN;
        if(i > 0 && l > 0)
        {
            int tmp = sum(i-1, j, k, l-1, memo);
            max = max < tmp ? tmp : max;
        }
        if(j > 0 && k > 0)
        {
            int tmp = sum(i, j-1, k-1, l, memo);
            max = max < tmp ? tmp : max;
        }
        return ans+max;
    }
}

int main(void)
{
    int n, x;
    scanf("%d", &n);
    grid.clear(); grid.resize(n);

    for(int i = 0;i < n;i++)
    {
        for(int j = 0;j < n;j++)
        {
            scanf("%d", &x);
            grid[i].push_back(x);
        }
    }
    memo.clear(); memo.resize(n, vector< vector< vector<int> > >(n, vector< vector<int> >(n, vector<int>(n, INT_MIN))));
    memo[0][0][0][n-1] = grid[0][0] + grid[0][n-1];

    int ans = sum(n-1, 0, n-1, n-1, memo);
    printf("%d\n", ans);
}