cf C. Tourist Problem

http://codeforces.com/contest/340/problem/C

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <algorithm>

 4 #define maxn 100010

 5 #define ll __int64

 6 using namespace std;

 7 

 8 ll a[maxn];

 9 int n;

10 

11 ll gcd(ll a,ll b)

12 {

13     return b==0?a:gcd(b,a%b);

14 }

15 

16 int main()

17 {

18     scanf("%d",&n);

19     ll ans=0;

20     for(int i=0; i<n; i++)

21     {

22         scanf("%I64d",&a[i]);

23         ans+=a[i];

24     }

25     sort(a,a+n);

26     for(int i=1; i<=n-1; i++)

27     {

28         ans+=(a[i]-a[i-1])*i*(n-i)*2;

29     }

30     int k=gcd(ans,n);

31     printf("%I64d %I64d\n",ans/k,(ll)n/k);

32     return 0;

33 }

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