1104 Sum of Number Segments (20 分)

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本文介绍了一种解决给定正数序列中所有连续子序列和问题的算法，通过实例演示如何计算每个子序列的和并求总和。重点在于C++代码实现，适用于理解区间和计算技巧。

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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.

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.

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
Thanks to Ruihan Zheng for correcting the test data.

#include<iostream>
#include<iomanip>
using namespace std;
int main() {
	int N;
	cin >> N;
	long long sum = 0.00;
	double temp;
	for (int i = 0; i < N; i++) {
		cin >> temp;
		sum = sum + (long long)(temp*1000) * (i + 1) * (N - i);
	}
	cout <<fixed<< setprecision(2) << sum/1000.0 << endl;
	return 0;
}