1 #include <bits/stdc++.h>
 using namespace std;
 #define rep(i, a, b) for (int i = a; i <= b; ++i)
 ;

 int n, a[N], f[N][N], ans;

 int main() {
     scanf("%d", &n);
     rep(i, , n) {
         scanf("%d", &a[i]);
         a[n + i] = a[i];
     }

     rep(len, , n + ) rep(i, , n *  - len + ) { ;
         rep(k, i + , j - ) {
             f[i][j] = max(f[i][j], f[i][k] + f[k][j] + a[i] * a[k] * a[j]);
         }
 //        cout << i << ' ' << j << ' ' << f[i][j] << '\n';
         ) ans = max(ans, f[i][j]);
     }

     printf("%d\n", ans);
     ;
 }

Tips:　　1.带样例彻底搞懂才开始思考　　1.想清楚len是n还是n+1(环形)