[数据结构-树状数组]POJ 2299 Ultra-QuickSort

#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;
int C[500005],n;
int lowbit(int x)
{
    return x&-x;
}
int sum(int x)      //求前缀和，x向左上爬
{
    int ret=0;
    while(x>0)
    {
        ret+=C[x];
        x-=lowbit(x);
    }
    return ret;
}
void add(int x,int d)     //A[x]加上d，x向右上爬
{
    while(x<=n)
    {
        C[x]+=d;
        x+=lowbit(x);
    }
}
struct D
{
    int id;
    long long val;
};
bool operator < (D a,D b)
{
    return a.val<b.val;
}
D data[500005];
int main()
{
    while(cin>>n&&n)
    {
        long long ans=0;
        for(int i=1; i<=n; i++)
        {
            cin>>data[i].val;
            data[i].id=i;
        }
        sort(data+1,data+n+1);
        data[0].val=-111;
        memset(C,0,sizeof(C));
        int pre;
        for(int i=1; i<=n; i++)
        {
            if(data[i].val!=data[i-1].val)
            {
                pre=sum(n)-sum(data[i].id);
                ans+=pre;
            }
            else ans+=pre;
            add(data[i].id,1);
        }
        cout<<ans<<endl;
    }
}