loj2013 「SCOI2016」幸运数字

点分治+线性基
（为了这六个字窝调了一下午一晚上QAQ

#include <iostream>
#include <cstring>
#include <cstdio>
#include <vector>
#include <cassert>
using namespace std;
typedef long long ll;
int n, uu, vv, m, hea[20005], cnt, sze, rot, rnd[20005], siz[20005], bel[20005];
bool vis[20005];
ll a[20005], ans[200005];
struct Edge{
	int too, nxt;
}edge[40005];
struct Ques{
	int u, v, idx;
};
struct LinearBase{
	ll num[65];
	void clear(){
		memset(num, 0, sizeof(num));
	}
	void insert(ll x){
		for(int i=60; i>=0; i--)
			if(x&(1ll<<i)){
				if(num[i])	x ^= num[i];
				else{
					num[i] = x;
					break;
				}
			}
	}
	ll operator+(const LinearBase &x)const{
		LinearBase c=x;
		for(int i=60; i>=0; i--)
			c.insert(num[i]);
		ll re=0;
		for(int i=60; i>=0; i--)
			if((re^c.num[i])>re)
				re ^= c.num[i];
		return re;
	}
}bas[20005];
vector<Ques> q[20005];
void add_edge(int fro, int too){
	edge[++cnt].nxt = hea[fro];
	edge[cnt].too = too;
	hea[fro] = cnt;
}
void getRoot(int x, int f){
	siz[x] = 1;
	rnd[x] = 0;
	for(int i=hea[x]; i; i=edge[i].nxt){
		int t=edge[i].too;
		if(t!=f && !vis[t]){
			getRoot(t, x);
			siz[x] += siz[t];
			rnd[x] = max(rnd[x], siz[t]);
		}
	}
	rnd[x] = max(rnd[x], sze-siz[x]);
	if(rnd[x]<rnd[rot])	rot = x;
}
void dfs1(int x, int f){
	bas[x].insert(a[x]);
	for(int i=hea[x]; i; i=edge[i].nxt){
		int t=edge[i].too;
		if(t!=f && !vis[t]){
			bas[t] = bas[x];
			dfs1(t, x);
		}
	}
}
void dfs2(int x, int f, int fro){
	bel[x] = fro;
	for(int i=hea[x]; i; i=edge[i].nxt){
		int t=edge[i].too;
		if(t!=f && !vis[t])	dfs2(t, x, fro);
	}
}
void work(int x){
	vis[x] = true;
	bas[x].clear();
	dfs1(x, 0);
	bel[x] = x;
	for(int i=hea[x]; i; i=edge[i].nxt){
		int t=edge[i].too;
		if(!vis[t])		dfs2(t, x, t);
	}
	for(int i=0; i<q[x].size(); i++)
		if(q[x][i].u==x || q[x][i].v==x || bel[q[x][i].u]!=bel[q[x][i].v])
			ans[q[x][i].idx] = bas[q[x][i].u] + bas[q[x][i].v];
		else
			q[bel[q[x][i].u]].push_back(q[x][i]);
	q[x].clear();
	for(int i=hea[x]; i; i=edge[i].nxt){
		int t=edge[i].too;
		if(!vis[t]){
			rot = 0;
			sze = siz[t];
			getRoot(t, 0);
			q[rot] = q[t];
			if(rot!=t)	q[t].clear();
			work(rot);
		}
	}
}
int main(){
	cin>>n>>m;
	for(int i=1; i<=n; i++)	scanf("%lld", &a[i]);
	for(int i=1; i<n; i++){
		scanf("%d %d", &uu, &vv);
		add_edge(uu, vv);
		add_edge(vv, uu);
	}
	sze = n;
	rnd[0] = 0x3f3f3f3f;
	getRoot(1, 0);
	for(int i=1; i<=m; i++){
		scanf("%d %d", &uu, &vv);
		if(uu==vv)	ans[i] = a[uu];
		else	q[rot].push_back((Ques){uu, vv, i});
	}
	work(rot);
	for(int i=1; i<=m; i++)
		printf("%lld\n", ans[i]);
	return 0;
}