poj 2299 Ultra-QuickSort(逆序对)

//树状数组
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <queue>
#include <cmath>
#include <string>
#include <cctype>
#include <map>
#include <iomanip>

using namespace std;

#define eps 1e-8
#define pi acos(-1.0)
#define inf 1<<30
#define linf 1LL<<60
#define pb push_back
#define lc(x) (x << 1)
#define rc(x) (x << 1 | 1)
#define lowbit(x) (x & (-x))
#define ll long long

struct Node
{
int v,x;
};

int c[500100],n;
int aa[500100];
Node a[500100];
ll ans;

bool cmp(const Node &a,const Node &b){
return a.v<b.v;
}

void update(int x,int val){
for(int i=x;i<=n;i+=lowbit(i)){
c[i]+=val;
}
}

int getsum(int x){
int temp=0;
for(int i=x;i>=1;i-=lowbit(i)){
temp+=c[i];
}
return temp;
}

int main(){
while(~scanf("%d",&n)){
if (n==0) break;
for (int i=1; i<=n; i++){
scanf("%d",&a[i].v);
a[i].x=i;
}
sort(a+1,a+n+1,cmp);
for (int i=1; i<=n; i++)
aa[a[i].x]=i;
memset(c,0,sizeof(c));
ans=0;
for (int i=1; i<=n; i++){
update(aa[i],1);
ans+=i-getsum(aa[i]);
}
printf("%lld\n",ans);
}
return 0;
}

//归并排序
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <queue>
#include <cmath>
#include <string>
#include <cctype>
#include <map>
#include <iomanip>

using namespace std;

#define eps 1e-8
#define pi acos(-1.0)
#define inf 1<<30
#define linf 1LL<<60
#define pb push_back
#define lc(x) (x << 1)
#define rc(x) (x << 1 | 1)
#define lowbit(x) (x & (-x))
#define ll long long

int a[500100],b[500100];
ll ans;
int n;

void solve_mergesort(int l,int r){
int i,j,k,m;
if (l>=r) return ;
m=(l+r)/2;
solve_mergesort(l,m);
solve_mergesort(m+1,r);
i=l;
j=m+1;
k=l;
do{
if (a[i]>a[j]){
b[k]=a[j];
ans+=m-i+1;
j++;
k++;
}
else{
b[k]=a[i];
k++;
i++;
}
} while (i<=m && j<=r);
while (i<=m){
b[k]=a[i];
k++;
i++;
}
while (j<=r){
b[k]=a[j];
k++;
j++;
}
for (int i=l; i<=r; i++) a[i]=b[i];
return ;
}

int main() {
while (~scanf("%d",&n)){
if (n==0) break;
for (int i=0; i<n; i++) scanf("%d",&a[i]);
ans=0;
solve_mergesort(0,n-1);
printf("%lld\n",ans);
}
return 0;
}