PAT 甲级 1104 sum of Number Segments

1104. Sum of Number Segments (20)

时间限制200 ms内存限制65536 kB代码长度限制16000 B判题程序Standard作者CAO, PengGiven 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 than1.0, 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

直接计算每个数出现了几次

公式：i*(n-i+1)

#include <iostream>#include <string.h>#include <algorithm>#include <math.h>#include <stdio.h>#include <stdlib.h>using namespace std;int n;double x;int main(){double ans;scanf("%d",&n);for(int i=1;i<=n;i++){scanf("%lf",&x);ans+=x*i*(n-i+1);}printf("%.2f\n",ans);return 0;}