poj2299：Ultra-QuickSort

求逆序对即可，然而发现还是bit容易写。。
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Ultra-QuickSort

Time Limit: 7000MS		Memory Limit: 65536K
Total Submissions: 49549		Accepted: 18142

Description

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define ll long long
#define rep(i,n) for(int i=1;i<=n;i++)
struct data{
ll w;int c;
bool operator<(const data&rhs)const {
return w<rhs.w;}
}e[500005];
int t[500005],n;
int lowbit(int x){return x&-x;}
void insert(int x){
for(int i=x;i<=n;i+=lowbit(i))
t[i]++;
}
int find(int x){
int tmp=0;
for(int i=x;i;i-=lowbit(i))
tmp+=t[i];
return tmp;
}
int main(){
while(scanf("%d",&n)&&n){
memset(t,0,sizeof(t));
rep(i,n){
scanf("%lld",&e[i].w);
e[i].c=i;
}
sort(e+1,e+n+1);
ll ans=0;
rep(i,n){
insert(e[i].c);
ans+=i-find(e[i].c);
}
printf("%lld\n",ans);
}
return 0;
}

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