可持久化Trie,大概和樹上主席樹一個做法
(竟然輕易地就1A了)
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#include<cmath>
using namespace std;
#define rep(i,l,r) for(int i=l;i<=r;i++)
#define per(i,r,l) for(int i=r;i>=l;i--)
#define mmt(a,v) memset(a,v,sizeof(a))
#define tra(i,u) for(int i=head[u];i;i=e[i].next)
const int N=100000+5;
int ch[N*20][2],sum[N*20];
int sz;
void insert(int &x,int y,int z){
sz++;ch[sz][0]=ch[x][0];ch[sz][1]=ch[x][1];sum[sz]=sum[x];x=sz;
sum[x]++;
if(!z)return;
int k=(y>>z-1)&1;
insert(ch[x][k],y,z-1);
}
int query(int u,int v,int w,int f,int z,int i){
if(!i)return 0;
int k=((z>>i-1)&1)^1;
if(sum[ch[u][k]]+sum[ch[v][k]]-sum[ch[w][k]]-sum[ch[f][k]])
return (1<<i-1)+query(ch[u][k],ch[v][k],ch[w][k],ch[f][k],z,i-1);
else return query(ch[u][k^1],ch[v][k^1],ch[w][k^1],ch[f][k^1],z,i-1);
}
struct Edge{int to,next;}e[N<<1];
int head[N],cnt;
void ins(int u,int v){e[++cnt]=(Edge){v,head[u]};head[u]=cnt;}
void insert(int u,int v){ins(u,v);ins(v,u);}
int fa[N],dep[N],son[N],top[N],siz[N];
int root[N],a[N];
void dfs(int u){
son[u]=0;siz[u]=1;
root[u]=root[fa[u]];
insert(root[u],a[u],16);
tra(i,u){
int v=e[i].to;if(v==fa[u])continue;
fa[v]=u;dep[v]=dep[u]+1;dfs(v);
siz[u]+=siz[v];if(siz[v]>siz[son[u]])son[u]=v;
}
}
void dfs(int u,int tp){
top[u]=tp;
if(son[u])dfs(son[u],tp);
tra(i,u){
int v=e[i].to;
if(v!=fa[u]&&v!=son[u])
dfs(v,v);
}
}
int lca(int u,int v){
while(top[u]!=top[v])
if(dep[top[u]]>dep[top[v]])u=fa[top[u]];
else v=fa[top[v]];
return dep[u]<dep[v]?u:v;
}
int query(int u,int v,int z){
int w=lca(u,v);
return query(root[u],root[v],root[w],root[fa[w]],z,16);
}
int main(){
//freopen("a.in","r",stdin);
int n,m;
while(~scanf("%d%d",&n,&m)){
mmt(head,0);cnt=0;
rep(i,1,n)scanf("%d",&a[i]);
rep(i,2,n){int u,v;scanf("%d%d",&u,&v);insert(u,v);}
root[0]=sz=0;ch[0][0]=ch[0][1]=sum[0]=0;
dfs(1);dfs(1,1);
while(m--){
int u,v,z;scanf("%d%d%d",&u,&v,&z);
printf("%d\n",query(u,v,z));
}
}
return 0;
}