P3605 [USACO17JAN]Promotion Counting P

求　　某节点子树内比该节点的点权大的点的个数

 

值域上维护树状数组，

#include <bits/stdc++.h>
using namespace std ;
 const int N=1e5+2,M=N*2;
 int bin[N],len;
 int sum[N] ,n,ans[N],a[N]; 
 
 int nxt[M],go[M],hd[N],all;
 
 void add_(int x,int y){
 	go[++all]=y,nxt[all]=hd[x];
	hd[x]=all;
 }
 int lowbit(int x){
 	return x&-x;
 } 
 int qq(int x){
 	int res= 0;
 	for(;x;x-=lowbit(x)) res+=sum[x];
 	return res; 
 }
 void add(int x,int v){
 	for(;x<=n;x+=lowbit(x)) sum[x]+=v ;
 }
 void dfs(int x){
 	ans[x]-= qq(n)-qq(a[x]);
 	
 	for(int i=hd[x];i;i=nxt[i]){
 		int y=go[i]; 
 		dfs(y);
 	}
 	
 	ans[x]+= qq(n)-qq(a[x]); 
 	add(a[x],1);
 }
 signed main(){ 
 	int i,x;
 	cin>>n;
 	for(i=1;i<=n;i++) cin>>a[i],bin[++len]=a[i];
 	sort(bin+1,bin+1+len);
 	len=unique(bin+1,bin+1+len)-bin-1;
 	for(i=1;i<=n;i++) 
 		a[i]=lower_bound(bin+1,bin+1+len,a[i])-bin;
 	
 	for(i=2;i<=n;i++) cin>>x,add_(x,i);
	dfs(1);
	for(i=1;i<=n;i++) cout<<ans[i]<<endl;
 }