PAT 1104 Sum of Number Segments （20 分）

1104 Sum of Number Segments （20 分）

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.

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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 $10^5$. The next line contains N positive numbers in the sequence, each no more than 1.0, separated by a space.

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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

解析

找规律题：多写几个数列就能看出规律了

#include<cstdio>
#include<vector>
using namespace std;
int main()
{
	int N;
	scanf("%d", &N);
	vector<double> data(N, 0.0);
	for (int i = 0; i < N; i++)
		scanf("%lf", &data[i]);
	double result = 0.0;
	for (int i = 0; i < N; i++)
		result += data[i] * (N - i)*(i + 1);
	printf("%.2f", result);

}