Topic links : https://pintia.cn/problem-sets/994805342720868352/problems/994805363914686464
题目描述
Given a sequence of positive numbers, a segment is defined to be a consecutive subsequence. For example, given the sequence { 0.1, 0.2, 0.3, 0.4 }, we have 10 segments: (0.1) (0.1, 0.2) (0.1, 0.2, 0.3) (0.1, 0.2, 0.3, 0.4) (0.2) (0.2, 0.3) (0.2, 0.3, 0.4) (0.3) (0.3, 0.4) and (0.4).
Now given a sequence, you are supposed to find the sum of all the numbers in all the segments. For the previous example, the sum of all the 10 segments is 0.1 + 0.3 + 0.6 + 1.0 + 0.2 + 0.5 + 0.9 + 0.3 + 0.7 + 0.4 = 5.0.
输入
Each input file contains one test case. For each case, the first line gives a positive integer N, the size of the sequence which is no more than 10^5 . The next line contains N positive numbers in the sequence, each no more than 1.0, separated by a space.
输出
For each test case, print in one line the sum of all the numbers in all the segments, accurate up to 2 decimal places.
Input Sample
4
0.1 0.2 0.3 0.4
Sample Output
5.00
Code
#include <cstdio>
int main() {
int n;
double sum = 0, a;
scanf("%d", &n);
for(int i = 1; i <= n; i++) {
scanf("%lf", &a);
sum += a * i * (n + 1 - i);
}
printf("%.2f\n", sum);
return 0;
}