【 [SCOI2016]幸运数字】

P3292 [SCOI2016]幸运数字

想法

倍增加上线性基就行惹

线性基的合并可以通过把一个线性基的元素插入到另一个里实现

#include<iostream>
#include<cstdio>
#include<cstring>
#define ll long long
#define N 20005
#define M 40005

ll cnt,v[N],G[N][21][62],head[N],dep[N];
ll fa[N][21],ans[62];

struct P{
	int to,next;
}e[M];

void add(int x,int y){
	e[++cnt].to = y;
	e[cnt].next = head[x];
	head[x] = cnt;
}

void insert(ll *a,ll val){
	for(int i = 61;i >= 0;--i){
		if((val >> i) & 1){
			if(!a[i]){
				a[i] = val;
				break;
			}
			val ^= a[i];
		}
	}
}

void Merge(ll *a,ll *b){
	for(int i = 61;i >= 0;--i){
		if(b[i])
		insert(a,b[i]);
	}
}

void dfs(ll u,ll f){
	fa[u][0] = f;
	dep[u] = dep[f] + 1;
	for(int i = head[u];i;i = e[i].next){
		ll v = e[i].to;
		if(v == f)
		continue;
		dfs(v,u);
	}
}

ll n,q;

void getlca(){
	for(int j = 1;j <= 20;++j)
	for(int i = 1;i <= n;++i){
		fa[i][j] = fa[fa[i][j - 1]][j - 1];
		std::memcpy(G[i][j],G[i][j - 1],sizeof(G[i][j - 1]));
		Merge(G[i][j],G[fa[i][j - 1]][j - 1]);
	}
}

void lca(ll x,ll y){
	if(dep[x] < dep[y])
	std::swap(x,y);
	for(int i = 20;i >= 0;--i){
		if(dep[fa[x][i]] >= dep[y]){
			Merge(ans,G[x][i]);
			x = fa[x][i];
		}
	}
	if(x == y){
		Merge(ans,G[x][0]);
		return;
	}
	for(int i = 20;i >= 0;--i){
		if(fa[x][i] != fa[y][i]){
			Merge(ans,G[x][i]);
			Merge(ans,G[y][i]);
			x = fa[x][i];
			y = fa[y][i];
		}
	}
	Merge(ans,G[x][0]),Merge(ans,G[y][0]),Merge(ans,G[fa[x][0]][0]);
	return;
}

inline ll read(){
	ll ans = 0,f = 1;
	char a = getchar();
	while(a < '0' && a > '9' && (a != '-'))
	a = getchar();
	if(a == '-')
	f = -1,a = getchar();
	while(a <= '9' && a >= '0'){
		ans = (ans << 3) + (ans << 1) + (a - '0'),a = getchar();
	}
	return ans * f;
}

int main(){
	n = read(),q = read();
	for(int i = 1;i <= n;++i)
	insert(G[i][0],read());
	for(int i = 1;i <= n - 1;++i){
		ll x = read(),y = read();
		add(x,y);
		add(y,x);
	}
	dfs(1,0);
	getlca();
	for(int i = 1;i <= q;++i){
		ll u = read(),v = read();
		std::memset(ans,0,sizeof(ans));
		lca(u,v);
		ll sum = 0;
		for(int i = 61;i >= 0;--i){
			if(ans[i])
			sum = std::max(sum,sum ^ (ans[i]));
		}
		std::cout<<sum<<std::endl;
	}
}