luogu 2982 [USACO10FEB]慢下来Slowing down dfs序+树状数组

#include <bits/stdc++.h>  
#define N 100004 
#define setIO(s) freopen(s".in","r",stdin) 
using namespace std;  
int n,edges,tim; 
int hd[N],to[N<<1],nex[N<<1],st[N],ed[N],C[N]; 
void add(int u,int v) 
{
    nex[++edges]=hd[u],hd[u]=edges,to[edges]=v; 
}  
int lowbit(int t) 
{
    return t&(-t); 
} 
void update(int x,int d) 
{ 
    for(;x<N;x+=lowbit(x)) C[x]+=d; 
} 
int query(int x) 
{
    int tmp=0; 
    for(;x>0;x-=lowbit(x)) tmp+=C[x]; 
    return tmp; 
}
void dfs(int u,int ff) 
{ 
    st[u]=++tim;    
    for(int i=hd[u];i;i=nex[i]) 
    {
        int v=to[i]; 
        if(v!=ff) dfs(v,u); 
    } 
    ed[u]=tim;  
}
int main() 
{  
    int i,j; 
    //setIO("input");  
    scanf("%d",&n);  
    for(i=1;i<n;++i) 
    {
        int u,v; 
        scanf("%d%d",&u,&v),add(u,v),add(v,u); 
    } 
    dfs(1,0);        
    for(i=1;i<=n;++i) 
    {  
        int p; 
        scanf("%d",&p);       
        printf("%d\n",query(st[p]));      
        update(st[p],1); 
        update(ed[p]+1,-1);        
    }
    // printf("%lld\n",ans); 
    return 0; 
}