先枚举长度的区间dp

#include <bits/stdc++.h>
#define maxn 300
using namespace std;
int n;
int a[maxn];
int f[maxn][maxn];

int main() {
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		if (i != n) {
			a[i + n] = a[i];
		}
	}
	for (int i = 1; i <= n * 2; i++) {
		f[i][i] = a[i];
	}
	for (int len = 2; len <= n + n - 1; len++) {
		for (int i = 1; i <= n + n - len + 1; i++) {
			int j = i + len - 1;
			for (int k = i; k < j; k++) {
				f[i][j] = max(f[i][j], f[i][k] + f[k + 1][j]);
			}
		}
	}
	cout << f[1][n];
	return 0;
}