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
#include<cstdio>const int maxn=100010;double a[maxn];int main(){ int n; double ans=0; scanf("%d",&n); for(int i=0;i<n;i++){ scanf("%lf",&a[i]); }// for(int i=0;i<n;i++){//此法会超时 // for(int j=i;j<n;j++){// ans+=a[j]*(n-j);// }// } for(int i=0;i<n;i++){ ans+=a[i]*(n-i)*(i+1); } printf("%.02lf",ans);}新闻热点
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