PAT-B 1049. 数列的片段和(20)

解题思路

AC代码

#include<cstdio>
#include<cstring>
#include<algorithm>

using namespace std;

int n;
double a[100010];

int main(){

scanf("%d",&n);

double sum = 0, temp;
for(int i = 0; i < n; i++){
scanf("%lf",&temp);
sum += temp*(i+1)*(n-i);
}

printf("%.2f\n",sum);

return 0;
}