【bzoj 4756】Promotion Counting（线段树合并）

#include<bits/stdc++.h>
#define N 100005
using namespace std;
int n,ans
;
struct Node{
Node*ch[2];
int L,R,sum;
Node(int l,int r){
L=l;R=r;
sum=0;
ch[0]=ch[1]=NULL;
}
Node(){}
void maintain(){
sum=0;
if(ch[0])   sum+=ch[0]->sum;
if(ch[1])   sum+=ch[1]->sum;
}
}*root
;
void Merge(Node* &x,Node* &y){
if(!y)  return;
if(!x){
x=y;
return;
}
x->sum+=y->sum;
Merge(x->ch[0],y->ch[0]);
Merge(x->ch[1],y->ch[1]);
}
void Insert(Node* &x,int v,int L,int R){
if(!x)  x=new Node(L,R);
if(x->L==x->R){
++x->sum;
return;
}
int mid=L+R>>1;
if(v<=mid)  Insert(x->ch[0],v,L,mid);
else        Insert(x->ch[1],v,mid+1,R);
x->maintain();
}
int Query(Node* x,int v){
if(!x)  return 0;
if(v==x->R)     return x->sum;
int mid=x->L+x->R>>1;
if(v<=mid)  return Query(x->ch[0],v);
return (x->ch[0] ? x->ch[0]->sum : 0) + Query(x->ch[1],v);
}
int a
,b
;
int head
,nex
,to
,tp;
void add(int x,int y){
nex[++tp]=head[x];
head[x]=tp;
to[tp]=y;
}
void dfs(int x){
for(int i=head[x];i;i=nex[i]){
dfs(to[i]);
Merge(root[x],root[to[i]]);
}
ans[x]=Query(root[x],n-a[x]);
Insert(root[x],n-a[x]+1,1,n);
}
int main(){
scanf("%d",&n);
for(int i=1;i<=n;++i)   scanf("%d",&a[i]),b[i]=a[i];
sort(b+1,b+n+1);
int m=unique(b+1,b+n+1)-b-1;
for(int i=1;i<=n;++i)   a[i]=lower_bound(b+1,b+m+1,a[i])-b;
for(int i=2;i<=n;++i){
int x;
scanf("%d",&x);
add(x,i);
}
dfs(1);
for(int i=1;i<=n;++i)   printf("%d\n",ans[i]);
return 0;
}