Blood Cousins CodeForces - 208E

http://codeforces.com/problemset/problem/208/E

问一个节点v有多少p兄弟 就等于看v的p祖先有多少p孩子

找p祖先就倍增或者树剖一下 然后就是某一层的节点中属于某棵子树的点有多少 用dfs序一判即可

#include <bits/stdc++.h>
using namespace std;
#define pb push_back
const int maxn=1e5+10;

struct node
{
    int v,next;
};

vector <int> pre[maxn];
node edge[maxn];
int first[maxn],fa[maxn],deep[maxn],sum[maxn],son[maxn],top[maxn],mp1[maxn],mp2[maxn];
int n,q,num;

void addedge(int u,int v)
{
    edge[num].v=v;
    edge[num].next=first[u];
    first[u]=num++;
}

void dfsI(int cur)
{
    int i,v;
    sum[cur]=1,son[cur]=-1;
    for(i=first[cur];i!=-1;i=edge[i].next){
        v=edge[i].v;
        if(v!=fa[cur]){
            deep[v]=deep[cur]+1;
            dfsI(v);
            sum[cur]+=sum[v];
            if(son[cur]==-1||sum[son[cur]]<sum[v]){
                son[cur]=v;
            }
        }
    }
}

void dfsII(int cur,int tp)
{
    int i,v;
    num++;
    top[cur]=tp,mp1[cur]=num,mp2[num]=cur;
    pre[deep[cur]].pb(mp1[cur]);
    if(son[cur]==-1) return;
    dfsII(son[cur],tp);
    for(i=first[cur];i!=-1;i=edge[i].next){
        v=edge[i].v;
        if(v!=fa[cur]&&v!=son[cur]){
            dfsII(v,v);
        }
    }
}

int getpos(int u,int dep)
{
    int tmp;
    while(deep[top[u]]>dep){
        u=fa[top[u]];
    }
    tmp=deep[u]-dep;
    return mp2[mp1[u]-tmp];
}

int main()
{
    int i,v,p,pl,pr,gou;
    scanf("%d",&n);
    memset(first,-1,sizeof(first));
    num=0;
    for(i=1;i<=n;i++){
        scanf("%d",&fa[i]);
        if(fa[i]!=0){
            addedge(fa[i],i);
        }
    }
    num=0;
    for(i=1;i<=n;i++){
        if(fa[i]==0){
            deep[i]=1;
            dfsI(i);
            dfsII(i,i);
        }
    }
    /*
    for(i=1;i<=n;i++){
        sort(pre[i].begin(),pre[i].end());
        for(int j=0;j<pre[i].size();j++){
            printf("%d ",pre[i][j]);
        }
        printf("\n");
    }
    */
    scanf("%d",&q);
    while(q--){
        scanf("%d%d",&v,&p);
        gou=deep[v];
        if(deep[v]-p<1){
            printf("0\n");
            continue;
        }
        v=getpos(v,deep[v]-p);
        //printf("***%d %d***\n",v,deep[v]);
        pl=lower_bound(pre[gou].begin(),pre[gou].end(),mp1[v])-pre[gou].begin();
        pr=upper_bound(pre[gou].begin(),pre[gou].end(),mp1[v]+sum[v]-1)-pre[gou].begin();
        printf("%d ",pr-pl-1);
    }
    printf("\n");
    return 0;
}