uva 10014 Simple calculations

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=955

根据递推公式推倒出a1的公式。

a1=(n*a0+an+1-2*(n*c1+(n-1)*c2+...+cn))/(n+1);

#include <cstdio>
#include <cstring>
#include <algorithm>
#define maxn 50000
using namespace std;

double a1,a2;
double c[maxn];
int t;
int n;

int main()
{
scanf("%d",&t);
while(t--)
{
scanf("%d",&n);
scanf("%lf%lf",&a1,&a2);
double sum=n*a1+a2;
for(int i=1; i<=n; i++)
{
scanf("%lf",&c[i]);
sum-=2.0*(n+1-i)*c[i];
}
printf("%.2lf\n",sum/(n+1));
if(t!=0) printf("\n");
}
return 0;
}

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