TIOJ 1908 (help me...)

//TIOJ 1908
#include <bits/stdc++.h>
using namespace std;

int arr[22][22];
int vis[22];
map<int, int> dp[22];
int n;

int dx[] = {-1,-1,-1,0,0,1,1,1};
int dy[] = {-1,0,1,-1,1,-1,0,1};

int dfs(int depth){
    if(depth == n * n)return 0;
    int x = depth / n;
    int y = depth % n;
    if(y == 0 && dp[x].find(vis[x]) != dp[x].end())return dp[x][vis[x]];
    int ret = 0;
    if(!(vis[x] & (1<<y))){
        vector<int> take;
        for(int i = 0 ; i < 8; ++i){
            int nx = x + dx[i], ny = y + dy[i];
            if(0 <= nx && nx < n && 0 <= ny && ny < n && !(vis[nx] & (1<<ny))){
                take.emplace_back(i);
                vis[nx] |= (1<<ny);
            }
        }
        vis[x] |= (1<<y);
        ret = dfs(depth+1) + arr[x][y];
        for(unsigned i = 0; i < take.size(); ++i){
            int nx = x + dx[take[i]], ny = y + dy[take[i]];
            vis[nx] &= ~(1<<ny);
        }
        vis[x] &= ~(1<<y);
    }
    if(x < 2 || y < 2 || (vis[x-2]&(1<<(y-2))))ret = max(ret, dfs(depth+1));
    if(y == 0)dp[x][vis[x]] = ret;
    return ret;
}

int32_t main(){
    cin >> n;
    for(int i = 0; i < n; ++i){
        for(int j = 0; j < n; ++j){
            cin >> arr[i][j];
        }
    }
    cout << dfs(0) << '\n';
    return 0;
}