hihocoder1821 取卡片游戏

思路：

博弈dp。

实现：

 1 #include <iostream>
 2 #include <algorithm>
 3 #include <cstring>
 4 using namespace std;
 5 typedef long long ll;
 6 
 7 const ll INF = 0x3f3f3f3f3f3f3f3f;
 8 int a[100005], n;
 9 ll dp[100005];
10 
11 ll dfs(int cur)
12 {
13     if (cur >= n) return 0;
14     if (dp[cur] != -1) return dp[cur];
15     ll sum = 0, ans = -INF;
16     for (int i = 0; i < 3; i++)
17     {
18         sum += a[cur + i];
19         ll minn = INF;
20         for (int j = 0; j < 3; j++)
21         {
22             minn = min(minn, dfs(cur + i + 1 + j + 1));
23         }
24         ans = max(ans, sum + minn);
25     }
26     return dp[cur] = ans;
27 }
28 
29 bool cmp(int a, int b)
30 {
31     return a > b;
32 }
33 
34 int main()
35 {
36     while (cin >> n)
37     {
38         memset(dp, -1, sizeof dp);
39         for (int i = 0; i < n; i++) cin >> a[i];
40         sort(a, a + n, cmp);
41         cout << dfs(0) << endl;
42     }
43     return 0;
44 }