Ultra-QuickSort

 1 #include<iostream>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<cstdio>
 5 #include<map>
 6 #include<vector>
 7 using namespace std;
 8 int n,a[500003],num;
 9 int c[500003];
10 int b[500003];
11 long long ans;
12 int lowbit(int x){
13     return x&(-x);
14 }
15 void add(int x){
16    while(x<=num){
17      c[x]+=1;
18      x+=lowbit(x);
19    }
20 }
21 int getsum(int x){
22    int sum=0;
23    while(x>=1){
24      sum+=c[x];
25      x-=lowbit(x);
26 
27    }
28    return sum;
29 }
30 int main(){
31    while(~scanf("%d",&n)&&n){
32        memset(c,0,sizeof(c));
33        memset(a,0,sizeof(a));
34        memset(b,0,sizeof(b));
35        ans=0;
36        for(int i=1;i<=n;i++){
37         scanf("%d",&a[i]);
38          b[i]=a[i];
39        }
40         sort(b+1,b+n+1);
41        num=unique(b+1,b+1+n)-b-1;
42        for(int i=n;i>=1;i--){
43            int temp=lower_bound(b+1,b+1+num,a[i])-b;
44           ans+=getsum(temp);
45           add(temp);
46        }
47        printf("%I64d\n",ans);
48    }
49 }