SGU-180-Feel Good

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int maxn=1e5+1000;
const int inf=1<<30;
int n,g[maxn];
struct Node
{
int val;
int id;
int index;
bool operator < (const Node &a)const{
return val<a.val;
}
}a[maxn];
int pos[maxn];
int lowbit(int x)
{
return x&(-x);
}
void Update(int x,int val)
{
for(;x<=n;x+=lowbit(x))
g[x]+=val;
}
int Sum(int x)
{
int ans=0;
for(;x>0;x-=lowbit(x))
ans+=g[x];
return ans;
}
int main()
{
while(scanf("%d",&n)!=EOF)
{
long long ans=0;
memset(g,0,sizeof(g));
for(int i=1;i<=n;i++)
{
a[i].index=i;
scanf("%d",&a[i].val);
}
sort(a+1,a+n+1);
int cnt=0;
for(int i=1;i<=n;i++)
{
if(i>1&&a[i].val==a[i-1].val)
pos[a[i].index]=cnt;
else
pos[a[i].index]=++cnt;
}
for(int i=1;i<=n;i++)
{
Update(pos[i],1);
ans+=i-Sum(pos[i]);
}
printf("%lld\n",ans);
}
return 0;
}