PAT 1104 Sum of Number Segments

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 1. 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<bits/stdc++.h>
using namespace std;
typedef long long ll;


int main(){
    int n;cin >> n;
    double sum = 0.0;
    for(int i=1;i <= n;i++){
        double x;cin >> x;

        sum+=i*(n+1-i)*x;
    }
    printf("%.2f",sum);

    return 0;
}

x放右面就过不了几个点，x放左边就能过了

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;


int main(){
    int n;cin >> n;
    double sum = 0.0;
    for(int i=1;i <= n;i++){
        double x;cin >> x;

        sum+=x*i*(n+1-i);
    }
    printf("%.2f",sum);

    return 0;
}

对拍了半小时也没啥不同，这个bug先欠着，以后记着把double放左边先乘