CF 208E

倍增求LCA模板

#include<cstdio>#include<cstring>#include<vector>#include<algorithm>#define N 100100using namespace std;vector<int>vec,vec1[N];int head[N],cnt;struct Edge{    int v,next;}edge[N];int tim,fa[N],b[N],son[N],dep[N],p[N][18];int ans[N];void init(){    vec.clear();    memset(head,-1,sizeof(head));    memset(dep,0,sizeof(dep));    memset(p,0,sizeof(p));    memset(son,0,sizeof(son));    cnt=tim=0;}void addedge(int u,int v){    edge[cnt].v=v;    edge[cnt].next=head[u];    head[u]=cnt++;}void dfs(int u){    int i;    b[u]=++tim;    dep[u]=dep[fa[u]]+1;    vec1[dep[u]].push_back(tim);    p[u][0]=fa[u];    for(i=1;i<18;i++)p[u][i]=p[p[u][i-1]][i-1];    son[u]=1;    for(i=head[u];i!=-1;i=edge[i].next){        int v=edge[i].v;        dfs(v);        son[u]+=son[v];    }}int find(int u,int num){    //返回u的第num代祖先    for(int i=0;i<18;i++)        if((1<<i)&num)            u=p[u][i];    return u;}int solve(int t,int num){   //二分查找区间[0,vec1[num].size()-1]内vec1[num][i]<=t中最大的i    int h=vec1[num].size()-1,l=0,sum=-1;    while(l<=h){        int mid=(h+l)>>1;        if(vec1[num][mid]>t)            h=mid-1;        else{            sum=mid;            l=mid+1;        }    }    return sum;}int main(){    int i,v,n,m,num;    init();    scanf("%d",&n);    for(i=1;i<=n;i++){        scanf("%d",&v);        fa[i]=v;        if(v==0)vec.push_back(i);        addedge(v,i);    }    for(i=0;i<vec.size();i++)        dfs(vec[i]);    scanf("%d",&m);    for(i=1;i<=m;i++){        scanf("%d %d",&v,&num);        int u=find(v,num);        if(!u)ans[i]=0;        else ans[i]=solve(b[u]+son[u]-1,dep[v])-solve(b[u]-1,dep[v])-1;    }    for(i=1;i<=m;i++)        if(i==1)printf("%d",ans[i]);        else printf(" %d",ans[i]);    printf("\n");return 0;}