BZOJ2588: Spoj 10628. Count on a tree

a[a[u].l].sum+a[a[v].l].sum-a[a[fa].l].sum-a[a[grandfa].l].sum

#include<iostream>
#include<algorithm>
#include<cstdio>
#define MAXN 100010
using namespace std;
int n,m,q,c=1;
int val[MAXN],num[MAXN],root[MAXN];
int head[MAXN],deep[MAXN],son[MAXN],size[MAXN],fa[MAXN],top[MAXN];
struct node1{
	int next,to;
}a[MAXN<<1];
inline int read(){
	int date=0,w=1;char c=0;
	while(c<‘0‘||c>‘9‘){if(c==‘-‘)w=-1;c=getchar();}
	while(c>=‘0‘&&c<=‘9‘){date=date*10+c-‘0‘;c=getchar();}
	return date*w;
}
namespace ST{
	int size=0;
	struct Segment{
		int l,r,sum;
	}a[MAXN*20];
	inline void buildtree(){
	    a[0].sum=a[0].l=a[0].r=root[0]=0;
	}
	void insert(int k,int l,int r,int &rt){
	    int mid;
	    a[++size]=a[rt];rt=size;
	    a[rt].sum++;
	    if(l==r)return;
	    mid=l+r>>1;
	    if(k<=mid)insert(k,l,mid,a[rt].l);
	    else insert(k,mid+1,r,a[rt].r);
	}
	int query(int u,int v,int fa,int grandfa,int l,int r,int k){
	    if(l==r)return l;
	    int mid=l+r>>1,t=a[a[u].l].sum+a[a[v].l].sum-a[a[fa].l].sum-a[a[grandfa].l].sum;
	    if(k<=t)return query(a[u].l,a[v].l,a[fa].l,a[grandfa].l,l,mid,k);
	    else return query(a[u].r,a[v].r,a[fa].r,a[grandfa].r,mid+1,r,k-t);
	}
}
inline void add(int x,int y){
    a[c].to=y;a[c].next=head[x];head[x]=c++;
    a[c].to=x;a[c].next=head[y];head[y]=c++;
}
void dfs1(int rt){
    son[rt]=0;size[rt]=1;
    for(int i=head[rt];i;i=a[i].next){
        int will=a[i].to;
        if(!deep[will]){
            deep[will]=deep[rt]+1;
            fa[will]=rt;
            dfs1(will);
            size[rt]+=size[will];
            if(size[son[rt]]<size[will])son[rt]=will;
        }
    }
}
void dfs2(int rt,int f){
    top[rt]=f;
    if(son[rt])dfs2(son[rt],f);
    for(int i=head[rt];i;i=a[i].next){
        int will=a[i].to;
        if(will!=fa[rt]&&will!=son[rt])
        dfs2(will,will);
    }
}
int LCA(int x,int y){
    while(top[x]!=top[y]){
        if(deep[top[x]]<deep[top[y]])swap(x,y);
        x=fa[top[x]];
    }
    if(deep[x]>deep[y])swap(x,y);
    return x;
}
void buildtree(int rt){
    int will;
    int x=lower_bound(num+1,num+q+1,val[rt])-num;
    root[rt]=root[fa[rt]];
    ST::insert(x,1,q,root[rt]);
    for(int i=head[rt];i;i=a[i].next){
        will=a[i].to;
        if(will==fa[rt])continue;
        buildtree(will);
    }
}
void work(){
    int x,y,k,last=0;
    while(m--){
        x=read()^last;y=read();k=read();
        int lca=LCA(x,y);
        last=num[ST::query(root[x],root[y],root[lca],root[fa[lca]],1,q,k)];
        printf("%d\n",last);
    }
}
void init(){
    int x,y;
    n=read();m=read();
    for(int i=1;i<=n;i++)num[i]=val[i]=read();
    sort(num+1,num+n+1);
    q=unique(num+1,num+n+1)-num-1;
    for(int i=1;i<n;i++){
        x=read();y=read();
        add(x,y);
    }
    deep[1]=1;
    dfs1(1);
    dfs2(1,1);
    ST::buildtree();
    buildtree(1);
}
int main(){
    init();
    work();
	return 0;
}