luogu2633 Count on a tree

主席树放到树上而已

#include <algorithm>
#include <iostream>
#include <cstdio>
using namespace std;
int n, m, lstans, uu, vv, a[100005], b[100005], rnk[100005], rem, cnt;
int lson[2200005], rson[2200005], sum[2200005], rot[100005], qwq, ww;
int fa[100005][19], dep[100005], hea[100005], tt[5];
struct Edge{
	int too, nxt;
}edge[200005];
void add_edge(int fro, int too){
	edge[++qwq].nxt = hea[fro];
	edge[qwq].too = too;
	hea[fro] = qwq;
}
int build(int l, int r){
	int rt=++cnt;
	int mid=(l+r)>>1;
	if(l==r)	return rt;
	if(l<=mid)	lson[rt] = build(l, mid);
	if(mid<r)	rson[rt] = build(mid+1, r);
	return rt;
}
int update(int pre, int l, int r, int x){
	int rt=++cnt;
	int mid=(l+r)>>1;
	lson[rt] = lson[pre]; rson[rt] = rson[pre]; sum[rt] = sum[pre] + 1;
	if(l<r){
		if(x<=mid)	lson[rt] = update(lson[pre], l, mid, x);
		if(mid<x)	rson[rt] = update(rson[pre], mid+1, r, x);
	}
	return rt;
}
void dfs(int x, int f){
	fa[x][0] = f;
	dep[x] = dep[f] + 1;
	rot[x] = update(rot[f], 1, rem, rnk[x]);
	for(int i=hea[x]; i; i=edge[i].nxt){
		int t=edge[i].too;
		if(t!=f)	dfs(t, x);
	}
}
int getLca(int uu, int vv){
	if(dep[uu]<dep[vv])	swap(uu, vv);
	for(int i=16; i>=0; i--)
		if(dep[fa[uu][i]]>=dep[vv])
			uu = fa[uu][i];
	if(uu==vv)	return vv;
	for(int i=16; i>=0; i--)
		if(fa[uu][i]!=fa[vv][i]){
			uu = fa[uu][i];
			vv = fa[vv][i];
		}
	return fa[uu][0];
}
int query(int l, int r, int k){
	int tmp=0;
	int mid=(l+r)>>1;
	tmp -= sum[lson[tt[3]]] + sum[lson[tt[4]]];
	tmp += sum[lson[tt[1]]] + sum[lson[tt[2]]];
	if(l==r)	return l;	
	if(k<=tmp){
		for(int i=1; i<=4; i++)
			tt[i] = lson[tt[i]];
		return query(l, mid, k);
	}
	else{
		for(int i=1; i<=4; i++)
			tt[i] = rson[tt[i]];
		return query(mid+1, r, k-tmp);
	}
}
int main(){
	cin>>n>>m;
	for(int i=1; i<=n; i++){
		scanf("%d", &a[i]);
		b[i] = a[i];
	}
	for(int i=1; i<n; i++){
		scanf("%d %d", &uu, &vv);
		add_edge(uu, vv);
		add_edge(vv, uu);
	}
	sort(b+1, b+1+n);
	rem = unique(b+1, b+1+n) - (b + 1);
	for(int i=1; i<=n; i++)
		rnk[i] = lower_bound(b+1, b+1+rem, a[i]) - b;
	rot[0] = build(1, rem);
	dfs(1, 0);
	for(int i=1; i<=16; i++)
		for(int j=1; j<=n; j++)
			fa[j][i] = fa[fa[j][i-1]][i-1];
	while(m--){
		scanf("%d %d %d", &uu, &vv, &ww);
		uu ^= lstans;
		int lca=getLca(uu, vv);
		tt[1] = rot[uu]; tt[2] =rot[vv];
		tt[3] = rot[lca]; tt[4] = rot[fa[lca][0]];
		lstans = b[query(1, rem, ww)];
		printf("%d\n", lstans);
	}
	return 0;
}