排序然后贪心吧，自己也有点忘记了。地址：http://acm.pku.edu.cn/JudgeOnline/problem?id=2231

#include "stdio.h"

__int64 num[10005];

void swap(int a,int b)
{
    __int64 t;
    t=num[a];
    num[a]=num[b];
    num[b]=t;

}

int partion(int low,int high,int p)
{
    while(low<=high)
    {
        if(low<p)
        {
            if(num[low]>num[p]){swap(low,p);p=low;}
            low++;
        }
        else
        {
            if(high>p)
            {
                if(num[high]<num[p]){swap(high,p);p=high;}
            }
            high--;
        }
    }
    return p;
}

void qsort(int left,int right)
{
    int middle;
    if(left<right)
    {
        middle=(left+right)/2;
        middle=partion(left,right,middle);
        qsort(left,middle-1);
        qsort(middle+1,right);
    }
}

int main()
{
    int n,i;
    __int64 value,sum;

    while(scanf("%d",&n)!=EOF)
    {
        for(i=0;i<n;i++)
        {
            scanf("%I64d",&num[i]);
        }

        qsort(0,n-1);

        value=0;
        for(i=0;i<n;i++)
        {
            value+=num[i]-num[0];
        }

        sum=value;
        for(i=1;i<n;i++)
        {
            value=value+(num[i]-num[i-1])*i-(num[i]-num[i-1])*(n-i);
            sum+=value;
        }

        printf("%I64d\n",sum);
    }
    return 0;
}