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 ;

 }