区间DP，破环成链

#include <bits/stdc++.h>
using namespace std;
const int N = 210, INF = 0x3f3f3f3f, MOD = 1E9 + 7;
int n, w[N], f[N][N];

int main() {
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> w[i], w[i + n] = w[i];
    }

    for (int len = 3; len <= n + 1; len++)
        for (int l = 1; l + len - 1 <= 2 * n; l++) {
            int r = l + len - 1;
            for (int k = l + 1; k < r; k++) {
                f[l][r] = max(f[l][r], f[l][k] + f[k][r] + w[l] * w[k] * w[r]);
            }
        }
    int res = 0;
    for (int i = 1; i <= n; i++)
        res = max(res, f[i][i + n]);
    cout << res;
    return 0;
}