hdu 3506 Monkey Party 区间dp + 四边形不等式优化

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <assert.h>
#define IOS ios::sync_with_stdio(false)
using namespace std;
#define inf (0x3f3f3f3f)
typedef long long int LL;


#include <iostream>
#include <sstream>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <string>
int n;
const int maxn = 2e3 + 20;
int dp[maxn][maxn];
int s[maxn][maxn];
int sum[maxn];
int a[maxn];
void work() {
    for (int i = 1; i <= n; ++i) {
        scanf("%d", &a[i]);
        a[i + n] = a[i];
    }
    n *= 2;
    for (int i = 1; i <= n; ++i) {
        dp[i][i] = 0;
        s[i][i] = i;
        sum[i] = sum[i - 1] + a[i];
    }
    for (int dis = 1; dis <= n - 1; ++dis) {
        for (int be = 1; be + dis <= n; ++be) {
            int en = be + dis;
            int tk = s[be][en];
            dp[be][en] = inf;
            for (int k = s[be][en - 1]; k <= s[be + 1][en]; ++k) {
                if (k + 1 > en) break;
                int add = dp[be][k] + dp[k + 1][en] + sum[en] - sum[be - 1];
                if (dp[be][en] > add) {
                    dp[be][en] = add;
                    tk = k;
                }
            }
            s[be][en] = tk;
        }
    }
    int ans = inf;
    for (int i = 1; i <= n / 2; ++i) {
        ans = min(ans, dp[i][i + n / 2 - 1]);
    }
    cout << ans << endl;
}
int main() {
#ifdef local
    freopen("data.txt", "r", stdin);
//    freopen("data.txt", "w", stdout);
#endif
    while (scanf("%d", &n) != EOF) work();
    return 0;
}