dp——环形石子合并（区间dp）

环形的解决很巧妙

 #include <iostream>
 #include <cstring>
 #include <string>
 #include <map>
 #include <set>
 #include <algorithm>
 #include <fstream>
 #include <cstdio>
 #include <cmath>
 #include <stack>
 #include <queue>
 #define lson l,m,rt<<1
 #define rson m+1,r,rt<<1|1
 using namespace std;
 const double Pi=3.14159265358979323846;
 typedef long long ll;
 const int MAXN=+;
 const int dx[]={,,,,-};
 const int dy[]={,-,,,};
 const int INF = 0x3f3f3f3f;
 const int NINF = 0xc0c0c0c0;
 const ll mod=1e9+;

 int a[MAXN*],dp[MAXN*][MAXN*];int sum[MAXN*];int df[MAXN*][MAXN*];

 int main()
 {
     int n;scanf("%d",&n);
     memset(dp,,sizeof(dp));
     for(int i=;i<=n;i++)
     {
         scanf("%d",&a[i]);
         sum[i]=sum[i-]+a[i];
     }
     for(int i=n+;i<=n+n;i++)
     {
         a[i]=a[i-n];

         sum[i]=sum[i-]+a[i];
     }
     for(int l=;l<=n;l++)
     {

         for(int i=;i<=n+n;i++)
         {
             int j=l+i-;
             df[i][j]=INF;
             if(j>n+n) continue;
             for(int k=i;k<j;k++)
             {
                 dp[i][j]=max(dp[i][k]+dp[k+][j]+sum[j]-sum[i-],dp[i][j]);
                 df[i][j]=min(df[i][k]+df[k+][j]+sum[j]-sum[i-],df[i][j]);
             }

         }
     }
     int ans1=;
     int ans2=INF;
     for(int i=;i<=n;i++)
     {
         int j=i+n-;
         if(j>n+n) break;
         ans1=max(dp[i][j],ans1);
         ans2=min(df[i][j],ans2);

     }
     cout << ans2<<endl<<ans1<<endl;
     return ;
 }