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);

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <algorithm>

 4 #define maxn 50000

 5 using namespace std;

 6 

 7 double a1,a2;

 8 double c[maxn];

 9 int t;

10 int n;

11 

12 int main()

13 {

14     scanf("%d",&t);

15     while(t--)

16     {

17         scanf("%d",&n);

18         scanf("%lf%lf",&a1,&a2);

19         double sum=n*a1+a2;

20         for(int i=1; i<=n; i++)

21         {

22             scanf("%lf",&c[i]);

23             sum-=2.0*(n+1-i)*c[i];

24         }

25         printf("%.2lf\n",sum/(n+1));

26         if(t!=0) printf("\n");

27     }

28     return 0;

29 }

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