poj 2299 Ultra-QuickSort(归并排序或是bit 树+离散化皆可)

#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<set>
#include<map>
#include<queue>
#include<vector>
#include<iterator>
#include<utility>
#include<sstream>
#include<iostream>
#include<cmath>
#include<stack>
using namespace std;
const int INF=1000000007;
const double eps=0.00000001;
typedef __int64 LL;
int N;
int A[500001],pos[500001],elem[500001];
int lowbit(int x){  return x&-x; }
int sum(int id)
{
    int ret=0;
    while(id>0){ ret+=elem[id]; id-=lowbit(id); }
    return ret;
}
void add(int id,int val)
{
    while(id<=N){ elem[id]+=val; id+=lowbit(id); }
}
vector<int> save;
int main()
{
    while(scanf("%d",&N)!=EOF&&N)
    {
        save.clear();
        memset(elem,0,sizeof(elem));
        for(int i=1;i<=N;i++)
        {
            scanf("%d",&A[i]);
            save.push_back(A[i]);
        }
        sort(save.begin(),save.end());

        for(int i=1;i<=N;i++)
        {
            pos[i]=lower_bound(save.begin(),save.end(),A[i])-save.begin()+1;   //离散化
        }
        LL ans=0;
        for(int i=1;i<=N;i++)
        {
           add(pos[i],1);   //插入这个数
           ans+=i-sum(pos[i]);    //计算逆序对个数

        }
        cout<<ans<<endl;
    }
    return 0;
}