题解 | 能量项链

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
const int N = 220;
const int Mod = 1e9 + 7;
ll a[N];
int n;
ll dp[N][N];

int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        scanf("%lld",&a[i]);
        a[i+n] =a[i];
    }

    for(int len=3;len<=n+1;len++){
        for(int i=1,j;(j=i+len-1)<=2*n;i++){
            for(int k =i+1;k<j;k++){//分割点
                dp[i][j] = max(dp[i][j],dp[i][k]+dp[k][j]+a[i]*a[k]*a[j]);
            }
        }
    }

    ll ans = 0;
    for(int i=1;i<=n;i++){
        ans = max(ans,dp[i][n+i]);
    }

    printf("%lld\n",ans%Mod);

    return 0;
}

聚环成链，然后区间dp

#牛客春招刷题训练营#https://www.nowcoder.com/discuss/727521113110073344