## Pat(A) 1104. Sum of Number Segments (20)

### 1104. Sum of Number Segments (20)

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) (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.

Input Specification:

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 105. The next line contains N positive numbers in the sequence, each no more than 1.0, separated by a space.

Output Specification:

For each test case, print in one line the sum of all the numbers in all the segments, accurate up to 2 decimal places.

Sample Input:
4
0.1 0.2 0.3 0.4

Sample Output:
5.00

1 0.1 4 4
2 0.2 3 3 6
3 0.3 2 2 2 6
4 0.4 1 1 1 1 4

### 代码

#include "iostream"
using namespace std;

int main(){
int n;
double x,sum = 0;
cin>>n;
for(int i = 1; i <= n; i++){
cin>>x;
sum += x * (n + 1 - i) * i;
}
printf("%.2lf\n",sum);
system("pause");
}

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