2018 蓝桥杯省赛 B 组模拟赛（一）数列求值（附推导过程）

题面链接:https://nanti.jisuanke.com/t/20688

网上的博客很多都没有详细推导过程，特意写一下我的。

 

 

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<string>
#include<algorithm>
#include<iostream>
#include<queue>
#include<map>
#include<cmath>
#include<set>
#include<stack>
#define ll long long
#define pb push_back
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)>(y)?(y):(x))
#define cls(name,x) memset(name,x,sizeof(name))
#define fs first
#define sc second
#define mp make_pair
#define L(x) (1<<x)
#define next Next
#define index Index
using namespace std;
const int inf=1e9+10;
const ll llinf=1e17+10;
const int maxn=1e3+10;
const int maxm=25e2+10;
const int mod=1e9+7;
int n;
double A0,Ana1;
double C[maxn];
double sumC[maxn];
int main()
{
    //freopen("in.txt","r",stdin);
    while(~scanf("%d",&n))
    {
        scanf("%lf %lf",&A0,&Ana1);
        fill(sumC,sumC+maxn,0.0);
        for(int i=1;i<=n;i++)
        {
            scanf("%lf",&C[i]);
            sumC[i]=sumC[i-1]+C[i];
        }
        double d1;
        double t=0;
        for(int i=1;i<=n;i++)
        {
            t+=2.0*sumC[i];
        }
        d1=(Ana1-A0-t)/(n+1);
        printf("%.2lf\n",d1+A0);
    }
	return 0;
}