poj 2299 Ultra-QuickSort

#include <iostream>           //求逆序对数,树状数组+离散化,ac
#include <algorithm>
using namespace std;
int tree[500001],list[500001],n,maxn=500000;
__int64 amount;
struct node 
{
    __int64 val;
    int id;
    bool operator<(const node& z)const
    {
        return val<z.val;
    }
}sequence[500001];

void hash()        //离散化
{
    for(int i=1;i<=n;++i)
    {
        scanf("%I64d",&sequence[i].val);
        sequence[i].id=i;
    }
    sort(sequence+1,sequence+n+1);
    for(int i=1;i<=n;++i)
    {
        list[sequence[i].id]=i;
    }
}
int lowbit(int x)
{
    return x&(-x);
}
void update(int x)
{
    while(x<=maxn)
    {
        tree[x]++;
        x+=lowbit(x);
    }
}
int getsum(int x)
{
    int s=0;
    while(x>0)
    {
        s+=tree[x];
        x-=lowbit(x);
    }
    return s;
}
int main()
{
    while(cin>>n&&n)
    {
        memset(tree,0,sizeof(tree));
        amount=0;
        hash();
        for(int i=1;i<=n;++i)
        {
            update(list[i]);
            amount+=i-getsum(list[i]);
        }
        printf("%I64d\n",amount);
    }
    return 0;
}

　　

#include <iostream>            //树状数组ac
#include <algorithm>
using namespace std;
int tree[500001],list[500001],n,maxn=500000;
__int64 amount;
struct node 
{
    __int64 val;
    int id;
    bool operator<(const node& z)const
    {
        return val<z.val;
    }
}sequence[500001];

void hash()
{
    for(int i=1;i<=n;++i)
    {
        scanf("%I64d",&sequence[i].val);
        sequence[i].id=i;
    }
    sort(sequence+1,sequence+n+1);
    for(int i=1;i<=n;++i)
    {
        list[sequence[i].id]=i;
    }
}
int lowbit(int x)
{
    return x&(-x);
}
void update(int x)        //update和getsum，跟上面的程序相反
{
    while(x>0)
    {
        tree[x]++;
        x-=lowbit(x);
    }
}
int getsum(int x)
{
    int s=0;
    while(x<=maxn)
    {
        s+=tree[x];
        x+=lowbit(x);
    }
    return s;
}
int main()
{
    while(cin>>n&&n)
    {
        memset(tree,0,sizeof(tree));
        amount=0;
        hash();
        for(int i=1;i<=n;++i)
        {
            amount+=getsum(list[i]);    //也与上面的相反
            update(list[i]);
        }
        printf("%I64d\n",amount);
    }
    return 0;
}

　　

#include <iostream>        //ac,求归并排序的逆序数
using namespace std;
__int64 list[500005],temp[500005],amount;
int n;
void merge_sort(int beg,int end)
{
    if(end==beg)
        return ;
    int mid=(beg+end)/2;
    merge_sort(beg,mid);
    merge_sort(mid+1,end);
    int p=beg,q=mid+1,t=beg;
    while(p<=mid||q<=end)
    {
        if(q>end||(p<=mid&&list[p]<list[q]))
            temp[t++]=list[p++];
        else
        {
            temp[t++]=list[q++];
            amount+=mid-p+1;
        }
    }
    for(int i=beg;i<=end;++i)
    {
        list[i]=temp[i];
    }
}
int main()
{
    while(cin>>n&&n)
    {
        amount=0;
        for(int i=0;i<n;++i)
            scanf("%I64d",&list[i]);
        merge_sort(0,n-1);
        printf("%I64d\n",amount);
    }
    return 0;
}