hihocoder1821 取卡片游戏

思路：

博弈dp。

实现：

 #include <iostream>
 #include <algorithm>
 #include <cstring>
 using namespace std;
 typedef long long ll;

 const ll INF = 0x3f3f3f3f3f3f3f3f;
 int a[], n;
 ll dp[];

 ll dfs(int cur)
 {
     if (cur >= n) return ;
     if (dp[cur] != -) return dp[cur];
     ll sum = , ans = -INF;
     for (int i = ; i < ; i++)
     {
         sum += a[cur + i];
         ll minn = INF;
         for (int j = ; j < ; j++)
         {
             minn = min(minn, dfs(cur + i +  + j + ));
         }
         ans = max(ans, sum + minn);
     }
     return dp[cur] = ans;
 }

 bool cmp(int a, int b)
 {
     return a > b;
 }

 int main()
 {
     while (cin >> n)
     {
         memset(dp, -, sizeof dp);
         for (int i = ; i < n; i++) cin >> a[i];
         sort(a, a + n, cmp);
         cout << dfs() << endl;
     }
     return ;
 }