codeforces 842D. Vitya and Strange Lesson

http://codeforces.com/contest/842/problem/D
思路：
我把数组中的数扔进字典树里，之后我记录下每个状态出现的次数。随后我们不需要去每次都把数组异或，我们把所有查询的数异或，

#include <bits/stdc++.h>#define maxs 2002020#define mme(i,j) memset(i,j,sizeof(i))#define pb push_back#define ll long long#define lala puts("Lalalala")#define ohMyLove ios::sync_with_stdio(false);cin.tie(NULL);using namespace std;const ll inf = LONG_LONG_MAX;int son[maxs][3],val[maxs];int rt,tot;void init(){    rt=0;    tot=1;    mme(son[rt],0);}void Insert(int x){    int now=rt,id;    for(int i=20; i>=0; i--)    {        id = ((x>>i)&1);        if(!son[now][id])            son[now][id]=tot++;        now = son[now][id];        val[now]++;    }}int query(int x){    int now=rt,id,ans=0;    for(int i=20; i>=0; i--)    {        id = ( (x>>i) & 1 );        if(!son[now][id])            return ans;        if(val[son[now][id]]==(1<<i))        {            ans|=(1<<i);            now = son[now][1-id];        }        else            now = son[now][id];    }    return ans;}map<int,int>mp;int main(){    ohMyLove;    int n,m;    while(~scanf("%d%d",&n,&m))    {        mp.clear();        int x;        init();        for(int i=1; i<=n; i++)        {            scanf("%d",&x);            if(mp[x]==0)                Insert(x);            mp[x]=1;        }        int y=0;        for(int i=1; i<=m; i++)        {            scanf("%d",&x);            y^=x;            printf("%d\n",query(y));        }    }    return 0;}