【bzoj 4756】Promotion Counting（线段树合并）

传送门biu~
对于每一个节点建一个权值线段树。遍历每一棵子树，然后将子树的线段树合并到自己的线段树上。

#include<bits/stdc++.h>#define N 100005using namespace std;int n,ans[N];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[N];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[N],b[N];int head[N],nex[N],to[N],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;}