bzoj2588 count on a tree

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int n,m,q,cnt,tot,val,lastans;
int head[100005];
int rt[100005];
int fa[100005];
int dep[100005];
int siz[100005];
int son[100005];
int grand[100005];
int ans[100005];
struct node{
    int v;
    int w;
    int id;
}poi[100005];
struct Tree{
    int num;
    int ls;
    int rs;
}tr[5000005];
struct Edge{
    int fr;
    int to;
    int nxt;
}edge[200005];
void init(){
    dep[1]=1;
    memset(head,-1,sizeof(head));
}
void addedge(int f,int t){
    cnt++;
    edge[cnt].fr=f;
    edge[cnt].to=t;
    edge[cnt].nxt=head[f];
    head[f]=cnt;
}
int cmp1(node a,node b){
    return a.v<b.v;
}
int cmp2(node a,node b){
    return a.id<b.id;
}
void insert(int &x,int y,int l,int r,int p){
    x=++tot;
    if(l==r){
        tr[x].num=tr[y].num+1;
        return;
    }
    int mid=(l+r)>>1;
    tr[x].ls=tr[y].ls;
    tr[x].rs=tr[y].rs;
    if(p<=mid)insert(tr[x].ls,tr[y].ls,l,mid,p);
    else insert(tr[x].rs,tr[y].rs,mid+1,r,p);
    tr[x].num=tr[tr[x].ls].num+tr[tr[x].rs].num;
}
void dfs1(int u){
    siz[u]=1;
    for(int i=head[u];i!=-1;i=edge[i].nxt){
        int v=edge[i].to;
        if(v==fa[u])continue;
        fa[v]=u;
        dep[v]=dep[u]+1;
        dfs1(v);
        siz[u]+=siz[v];
        if(siz[v]>siz[son[u]]){
            son[u]=siz[v];
        }
    }
}
void dfs2(int u){
    if(u!=son[fa[u]])grand[u]=u;
    else grand[u]=grand[fa[u]];
    for(int i=head[u];i!=-1;i=edge[i].nxt){
        int v=edge[i].to;
        if(v==fa[u])continue;
        dfs2(v);
    }
}
void dfs3(int u){
    insert(rt[u],rt[fa[u]],1,val,poi[u].w);
    for(int i=head[u];i!=-1;i=edge[i].nxt){
        int v=edge[i].to;
        if(v==fa[u])continue;
        dfs3(v);
    }
}
int lca(int x,int y){
    while(grand[x]!=grand[y]){
        if(dep[grand[x]]<dep[grand[y]]){
            swap(x,y);
        }
        x=fa[grand[x]];
    }
    if(dep[x]>dep[y]){
        swap(x,y);
    }
    return x;
}
int query(int u,int v,int f,int g,int l,int r,int k){
    if(l==r){
        return ans[l];
    }
    int mid=(l+r)>>1;
    int num=tr[tr[u].ls].num+tr[tr[v].ls].num-tr[tr[f].ls].num-tr[tr[g].ls].num;
    if(k<=num){
        return query(tr[u].ls,tr[v].ls,tr[f].ls,tr[g].ls,l,mid,k);
    }
    else{
        return query(tr[u].rs,tr[v].rs,tr[f].rs,tr[g].rs,mid+1,r,k-num);
    }
}
int main(){
    init();
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++){
        scanf("%d",&poi[i].v);
        poi[i].id=i;
    }
    poi[0].v=-1;
    sort(poi+1,poi+n+1,cmp1);
    for(int i=1;i<=n;i++){
        if(poi[i].v!=poi[i-1].v){
            val++;
            ans[val]=poi[i].v;
        }
        poi[i].w=val;
    }
    sort(poi+1,poi+n+1,cmp2);
    for(int i=1;i<n;i++){
        int u,v;
        scanf("%d%d",&u,&v);
        addedge(u,v);
        addedge(v,u);
    }
    dfs1(1);
    dfs2(1);
    dfs3(1);
    for(int i=1;i<=m;i++){
        int u,v,k,f,g;
        scanf("%d%d%d",&u,&v,&k);
        u^=lastans;
        f=lca(u,v);
        g=fa[f];
        lastans=query(rt[u],rt[v],rt[f],rt[g],1,val,k);
        printf("%d",lastans);
        if(i!=m){
            printf("\n");
        }
    }
    return 0;
}