hdu 5086 数列连续和求和

http://acm.hdu.edu.cn/showproblem.php?pid=5086

求一段数列里面所有连续和的和，卡精度

规律很明显，数列里面每个数都被加了i*(n+1-i)次

注意下精度即可

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <string>
#include <queue>
#include <map>
#include <iostream>
#include <algorithm>
using namespace std;
#define RD(x) scanf("%I64d",&x)
#define RD2(x,y) scanf("%d%d",&x,&y)
#define RD3(x,y,z) scanf("%d%d%d",&x,&y,&z)
#define clr0(x) memset(x,0,sizeof(x))
#define clr1(x) memset(x,-1,sizeof(x))
#define eps 1e-9
const double pi = acos(-1.0);
typedef long long LL;
typedef unsigned long long ULL;
const int modo = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const int inf = 0x3fffffff;
const LL _inf = 1e18;
const int maxn = 500000,maxm = 10005;
#define mod 1000000007
LL s[maxn];
int main()
{
    int _;RD(_);
    LL n;
    while(_--){
        RD(n);
        for(int i = 1;i <= n;++i)
            RD(s[i]);
        LL ans = 0;
        for(LL i = 1;i <= n;++i){
            LL x = i * s[i] % mod;
            LL y = x * (n+1-i) % mod;
            ans = (ans + y) % mod;
        }
        printf("%I64d\n",ans);
    }
    return 0;
}