不太理解这个代码。。。

1 #include 
      
        2 #include 
       
         3 int map[32][32],v[32]; 4 int n,max; 5 void dfs(int row,int sum) 6 { 7  8     int ans = sum; 9     v[row] = 1;10     for (int i = 1; i <= n; i ++)11     {12         if (v[i]==0)13             ans += map[row][i];14         else15             ans -= map[row][i];16     }17     if (ans > max)18         max = ans;19     for (int i = row+1; i <= n; i ++)20     {21         if (ans > sum)22         {23             dfs(i,ans);24             v[i] = 0;25         }26     }27 }28 int main()29 {30     scanf("%d",&n);31     max = 0;32     memset(v,0,sizeof(v));33     for (int i = 1; i <= n; i ++)34     {35         for (int j = 1; j <= n; j ++)36         {37             scanf("%d",&map[i][j]);38         }39     }40     dfs(1,0);41     printf("%d\n",max);42     return 0;43 44 }