思路：

　　

 

代码：

#include 
     
      using namespace std;#define maxn 20005#define ll long longstruct DataType {    ll d[61],p[61];    ll cnt;    DataType()    {        memset(d,0,sizeof(d));        memset(p,0,sizeof(p));        cnt=0;    }    bool insert(long long val)    {        for(ll i=60;i>=0;i--)        {            if(val&(1LL<
      
       0;    }    ll Max()    {        ll res=0;        for(ll i=60;i>=0;i--)        {            if((res^d[i])>res) res^=d[i];        }        return res;    }};struct DataType ans;struct TreeNodeType {    ll l,r,mid;    DataType data;};struct TreeNodeType tree[maxn<<2];ll n,m,deep[maxn],id[maxn],size[maxn],f[maxn],head[maxn];ll E[maxn<<1],V[maxn<<1],tot,ai[maxn],bi[maxn],lar[maxn];ll top[maxn];inline void in(ll &now){    char Cget=getchar();now=0;    while(Cget>'9'||Cget<'0')Cget=getchar();    while(Cget>='0'&&Cget<='9')    {        now=now*10+Cget-'0';        Cget=getchar();    }}void edge_add(ll u,ll v){    E[++tot]=head[u],V[tot]=v,head[u]=tot;    E[++tot]=head[v],V[tot]=u,head[v]=tot;}void merge(DataType &a,DataType b){    for(ll i=0;i<=60;i++)    {        if(b.d[i]) a.insert(b.d[i]);    }}void dfs1(ll now,ll fa){    f[now]=fa,deep[now]=deep[fa]+1,size[now]=1;    for(ll i=head[now];i;i=E[i])    {        if(V[i]==fa) continue;        dfs1(V[i],now),size[now]+=size[V[i]];        if(size[lar[now]]
       
        >1;    build(now<<1,l,tree[now].mid),build(now<<1|1,tree[now].mid+1,r);    tree[now].data=tree[now<<1].data;    merge(tree[now].data,tree[now<<1|1].data);}void query(ll now,ll l,ll r){    if(tree[now].l>=l&&tree[now].r<=r)    {        merge(ans,tree[now].data);        return;    }    if(l<=tree[now].mid) query(now<<1,l,r);    if(r>tree[now].mid) query(now<<1|1,l,r);}ll query(ll x,ll y){    for(int i=0;i<=60;i++) ans.d[i]=0,ans.p[i]=0;    ans.cnt=0;    while(top[x]!=top[y])    {        if(deep[top[x]]
        
         deep[y]) swap(x,y);    query(1,id[x],id[y]);    return ans.Max();}int main(){    freopen("data.txt","r",stdin);    in(n),in(m);ll u,v;    for(ll i=1;i<=n;i++) in(ai[i]);    for(ll i=1;i