poj 2299 Ultra-QuickSort(线段树/树状数组/归并 求逆序对)

Problem: 2299		User: shu_dayang
Memory: 7380K		Time: 500MS
Language: C++		Result: Accepted
Source Code
//树状数组
#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
typedef long long LL;
#define MAXN  500005
#define MID(l,r) ((l + r) >> 1)
using namespace std;

int c[MAXN],aa[MAXN];
int n;

struct Node
{
    int val;
    int order;
}a[MAXN];

bool cmp(Node a, Node b)
{
    return a.val < b.val;
}

int lowbit(int x)
{
    return x &(-x);
}

void update(int x)
{
    while(x <= n)
    {
        c[x] += 1;
        x += lowbit(x);
    }
}

int query(int x)
{
    int sum = 0;
    while(x > 0)
    {
        sum += c[x];
        x -= lowbit(x);
    }
    return sum;
}

int main()
{
    LL ans;
    while(~scanf("%d",&n) && n != 0)
    {
        memset(c,0,sizeof(c));
        for(int i = 1; i <= n; i++)
        {
            scanf("%d",&a[i].val);
            a[i].order = i;
        }
        sort(a+1,a+1+n,cmp);
        for(int i = 1; i <= n; i++)
            aa[a[i].order] = i;

        ans = 0;
        for(int i = 1; i <= n; i++)
        {
            update(aa[i]);
            ans += i - query(aa[i]);
        }
        printf("%I64d\n",ans);
    }
    return 0;
}