解题：洛谷2633 Count on a tree

题面

在树上建主席树......

每个点从父亲那里建过来，最后建出来就是从根到$i$这条链上的主席树，查询的时候一边差分一边查询

($cmt[u]+cmt[v]-cmt[lca(u,v)]-cmt[anc[lca(u,v)]]$)

 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 using namespace std;
 const int N=,K=;
 int p[N],noww[*N],goal[*N];
 int siz[N],anc[N],dep[N],imp[N],top[N];
 int num[N],tep[N],cmt[N*K],son[N*K][],sum[N*K],uni[N*K];
 int n,m,t1,t2,t3,lca,cnt,tot,len,xnt,ans,n1,n2,n3,n4;
 void link(int f,int t)
 {
     noww[++cnt]=p[f];
     goal[cnt]=t,p[f]=cnt;
 }
 int Create(int pre,int l,int r,int pos)
 {
     int nde=++xnt;
     son[nde][]=son[pre][];
     son[nde][]=son[pre][];
     sum[nde]=sum[pre]+;
     if(l<r)
     {
         int mid=(l+r)/;
         if(pos<=mid) son[nde][]=Create(son[pre][],l,mid,pos);
         else son[nde][]=Create(son[pre][],mid+,r,pos);
     }
     return nde;
 }
 int Query(int l,int r,int rnk)
 {
     if(l==r) return l;
     int mid=(l+r)/,noww=sum[son[n1][]];
     noww+=sum[son[n2][]]-sum[son[n3][]]-sum[son[n4][]];
     if(rnk<=noww)
     {
         n1=son[n1][],n2=son[n2][],n3=son[n3][],n4=son[n4][];
         return Query(l,mid,rnk);
     }
     else
     {
         n1=son[n1][],n2=son[n2][],n3=son[n3][],n4=son[n4][];
         return Query(mid+,r,rnk-noww);
     }
 }
 void DFS(int nde,int fth,int dth)
 {
     int tmp=;
     siz[nde]=,dep[nde]=dth,anc[nde]=fth;
     cmt[nde]=Create(cmt[anc[nde]],,len,num[nde]);
     for(int i=p[nde];i;i=noww[i])
         if(goal[i]!=fth)
         {
             DFS(goal[i],nde,dth+);
             siz[nde]+=siz[goal[i]];
             if(siz[goal[i]]>tmp)
                 tmp=siz[goal[i]],imp[nde]=goal[i];
         }
 }
 void MARK(int nde,int tpp)
 {
     top[nde]=tpp;
     if(imp[nde])
     {
         MARK(imp[nde],tpp);
         for(int i=p[nde];i;i=noww[i])
             if(goal[i]!=anc[nde]&&goal[i]!=imp[nde])
                 MARK(goal[i],goal[i]);
     }
 }
 int LCA(int x,int y)
 {
     while(top[x]!=top[y])
     {
         if(dep[top[x]]<dep[top[y]])
             swap(x,y); x=anc[top[x]];
     }
     return dep[x]<dep[y]?x:y;
 }
 int main ()
 {
     scanf("%d%d",&n,&m);
     for(int i=;i<=n;i++)
         scanf("%d",&num[i]),tep[i]=num[i];
     sort(tep+,tep++n),len=unique(tep+,tep++n)-tep-;
     for(int i=;i<=n;i++)
         num[i]=lower_bound(tep+,tep++len,num[i])-tep;
     for(int i=;i<n;i++)
         scanf("%d%d",&t1,&t2),link(t1,t2),link(t2,t1);
     DFS(,,); MARK(,);
     for(int i=;i<=m;i++)
     {
         scanf("%d%d%d",&t1,&t2,&t3),t1^=ans,lca=LCA(t1,t2);
         n1=cmt[t1],n2=cmt[t2],n3=cmt[lca],n4=cmt[anc[lca]];
         printf("%d\n",ans=tep[Query(,len,t3)]);
     }
     return ;
 }