pku 2231 Moo Volume 선형 방법구sig(sig|a[i]-a[j]|)

Moo Volume
Time Limit: 1000MS
 
Memory Limit: 65536K
Total Submissions: 12801
 
Accepted: 3690
Description
Farmer John has received a noise complaint from his neighbor, Farmer Bob, stating that his cows are making too much noise. 
FJ's N cows (1 <= N <= 10,000) all graze at various locations on a long one-dimensional pasture. The cows are very chatty animals. Every pair of cows simultaneously carries on a conversation (so every cow is simultaneously MOOing at all of the N-1 other cows). When cow i MOOs at cow j, the volume of this MOO must be equal to the distance between i and j, in order for j to be able to hear the MOO at all. Please help FJ compute the total volume of sound being generated by all N*(N-1) simultaneous MOOing sessions.
Input
* Line 1: N 
* Lines 2..N+1: The location of each cow (in the range 0..1,000,000,000).
Output
There are five cows at locations 1, 5, 3, 2, and 4.
Sample Input

5
1
5
3
2
4

Sample Output

40

Hint
INPUT DETAILS: 
There are five cows at locations 1, 5, 3, 2, and 4. 
OUTPUT DETAILS: 
Cow at 1 contributes 1+2+3+4=10, cow at 5 contributes 4+3+2+1=10, cow at 3 contributes 2+1+1+2=6, cow at 2 contributes 1+1+2+3=7, and cow at 4 contributes 3+2+1+1=7. The total volume is (10+10+6+7+7) = 40.
#include
#include
#include
using namespace std;
long long a[11000];
int main()
{
    int n;
    while(scanf("%d",&n)==1)
    {
        for(int i=1;i<=n;i++) cin>>a[i];
        sort(a+1,a+1+n);
        long long sum=0;
        for(int i=1;i        {
            int j=i+1;
            sum+=i*(n-i)*(a[j]-a[i]);
        }
        sum*=2;
        cout<    }
    return 0;
}