【BZOJ】4756: [Usaco2017 Jan]Promotion Counting

#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
const int maxn=200010;
int n,first[maxn],cnt,tot,tots,root[maxn],a[maxn],b[maxn],ans[maxn];
struct edge{int v,from;}e[maxn*2];
void ins(int u,int v){tots++;e[tots].v=v;e[tots].from=first[u];first[u]=tots;}
struct cyc{int l,r,sum;}t[maxn*10];
void insert(int l,int r,int &x,int y){
    if(!x)x=++cnt;t[x].sum++;
    if(l==r)return;//
    int mid=(l+r)>>1;
    if(y<=mid)insert(l,mid,t[x].l,y);
    else insert(mid+1,r,t[x].r,y);
}
int merge(int x,int y){
    if(!x||!y)return x^y;//1
    t[x].l=merge(t[x].l,t[y].l);
    t[x].r=merge(t[x].r,t[y].r);//2
    t[x].sum=t[t[x].l].sum+t[t[x].r].sum;//3
    return x;
}
int ask(int left,int right,int k,int l,int r){
    if(l<=left&&right<=r)return t[k].sum;
    else{
        int mid=(left+right)>>1,sum=0;
        if(l<=mid)sum=ask(left,mid,t[k].l,l,r);
        if(r>mid)sum+=ask(mid+1,right,t[k].r,l,r);
        return sum;
    }
}
void dfs(int x){
    insert(1,tot,root[x],a[x]);
    for(int i=first[x];i;i=e[i].from){
        dfs(e[i].v);
        root[x]=merge(root[x],root[e[i].v]);
    }
    if(a[x]<tot)ans[x]=ask(1,tot,root[x],a[x]+1,tot);
}
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
        b[i]=a[i];
    }
    for(int i=2;i<=n;i++){
        int fa;scanf("%d",&fa);
        ins(fa,i);
    }
    sort(b+1,b+n+1);tot=n;
    tot=unique(b+1,b+tot+1)-b-1;
    for(int i=1;i<=n;i++)a[i]=lower_bound(b+1,b+tot+1,a[i])-b;
    dfs(1);
    for(int i=1;i<=n;i++)printf("%d\n",ans[i]);
    return 0;
}