Ultra-QuickSort（树状数组+离散化） POJ - 2299

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<cstring>
#include<stdio.h>
#include<algorithm>
#include<map>
#include<queue>
#include<set>
#include <sstream>
#include<vector>
#include<cmath>    
#include<stack>
#include<time.h>
#include<ctime>
using namespace std;
#define inf 1<<30
#define eps 1e-7
#define LD long double
#define LL long long
#define maxn 1000005
struct node
{
    int v, f;
}b[maxn];
int aa[maxn], c[maxn], n;
bool cmp(node A, node B)
{
    return A.v < B.v;
}
int low(int x)
{
    return x & (-x);
}
void updata(int p, int q)
{
    while (p <= n)
    {
        c[p] += q;
        p += low(p);
    }
}
int sum(int p)
{
    int ans = 0;
    while (p > 0)
    {
        ans += c[p];
        p -= low(p);
    }
    return ans;
}
int main()
{
    while (~scanf("%d", &n) )
    {
        if (n == 0)break;
        int i;
        LL ans = 0;
        for (i = 1; i <= n; i++)
        {
            scanf("%d", &b[i].v);
            b[i].f = i;
        }
        sort(b + 1, b+n+1, cmp);
        for (i = 1; i <= n; i++)
        {
            aa[b[i].f] = i;
        }
        memset(c, 0, sizeof(c));
        for (i = 1; i <= n; i++)
        {
            updata(aa[i], 1);
            ans += i - sum(aa[i]);
        }
        printf("%lld\n", ans);
    }
}