BZOJ 3295 动态逆序对 CDQ分治

这就是我声明中说的那道CDQ题目...

在经过一番重写之后,我A了.

至于题解,网上的题解写的都不错.

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<ctime>
#include<string>
#include<iomanip>
#include<algorithm>
#include<map>
using namespace std;
#define LL long long
#define FILE "dealing"
#define up(i,j,n) for(int i=j;i<=n;++i)
#define db double
#define ull unsigned long long
#define eps 1e-10
#define pii pair<int,int>
int read(){
	int x=0,f=1,ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+ch-'0';ch=getchar();}
	return f*x;
}
const int maxn=200010,maxm=20000,limit=1e6,inf=(int)(2e9),mod=(int)(7+1e9+0.1);
template<class T>bool cmax(T& a,T b){return a<b?a=b,true:false;}
template<class T>bool cmin(T& a,T b){return a>b?a=b,true:false;}
template<class T>T min(T& a,T& b){return a<b?a:b;}
template<class T>T max(T& a,T& b){return a>b?a:b;}
int n,m;
struct node{
	int v,t,id;
	LL ans;
}a[maxn],w[maxn];
int id[maxn],c[maxn];
int lowbit(int x){return x&-x;}
int getsum(int x){
	int ans=0;
	while(x){
		ans+=c[x];
		x-=lowbit(x);
	}
	return ans;
}
void add(int x,int d){
	while(x<=n){
		c[x]+=d;
		x+=lowbit(x);
	}
}
void init(){
	n=read(),m=read();int top=n;
	up(i,1,n)a[i].v=read(),id[a[i].v]=i,a[i].id=i;
	up(i,1,m){
		int v=read();
		a[id[v]].t=top--;
	}
	up(i,1,n)if(!a[i].t)a[i].t=top--;
}
bool cmp3(node a,node b){return a.id<b.id;}
int q[maxn],top=0;
void cdq(int l,int r){
	if(l==r)return;
	int mid=(l+r)>>1;
	cdq(l,mid);
	cdq(mid+1,r);
	int pos1=l,pos2=mid+1;
	while(pos1<=mid||pos2<=r){
		if((a[pos1].id<a[pos2].id&&pos1<=mid)||pos2>r){
			add(n-a[pos1].v+1,1);
			q[++top]=n-a[pos1].v+1;
			pos1++;
			continue;
		}
		if((a[pos1].id>a[pos2].id&&pos2<=r)||pos1>mid){
			a[pos2].ans+=getsum(n-a[pos2].v+1);
			pos2++;
		}
	}
	while(top)add(q[top--],-1);
	pos1=mid,pos2=r;
	while(pos1>=l||pos2>=mid+1){
		if((a[pos1].id>a[pos2].id&&pos1>=l)||(pos2<mid+1)){
			add(a[pos1].v,1);
			q[++top]=a[pos1].v;
			pos1--;
			continue;
		}
		if((a[pos1].id<a[pos2].id&&pos2>=mid+1)||(pos1<l)){
			a[pos2].ans+=getsum(a[pos2].v);
			pos2--;
		}
	}
	while(top)add(q[top--],-1);
	pos1=l,pos2=mid+1;int u=l-1;
	while(pos1<=mid||pos2<=r){
		if((a[pos1].id<a[pos2].id&&pos1<=mid)||pos2>r){
			w[++u]=a[pos1];
			pos1++;
			continue;
		}
		if((a[pos1].id>a[pos2].id&&pos2<=r)||pos1>mid){
			w[++u]=a[pos2];
			pos2++;
		}
	}
	up(i,l,r)a[i]=w[i];
}
bool cmp(node a,node b){return a.t<b.t;}
LL ans[maxn];
void solve(){
	sort(a+1,a+n+1,cmp);
	cdq(1,n);
	sort(a+1,a+n+1,cmp);
	up(i,1,n)ans[i]=ans[i-1]+a[i].ans;
	for(int i=n;i>=n-m+1;i--)printf("%lld\n",ans[i]);
}
int main(){
	freopen(FILE".in","r",stdin);
	freopen(FILE".out","w",stdout);
	init();
	solve();
	return 0;
}