CF703D Mishka and Interesting sum

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<map>
using namespace std;
int n,m;
int a[1000005];
struct qu{
    int l;
    int r;
    int num;
}qj[1000005];
map<int,int>fl;
bool cmp(qu x,qu y){
    return x.r<y.r;
}
int tree[1000005];
int ans[1000005];
int sum1[1000005];
int lowbit(int x){
    return x&-x;
}
void add(int x,int k){
    while(x<=n){
        tree[x]^=k;
        x+=lowbit(x);
    }
    return ;
}
int sum(int x){
    int ans=0;
    while(x){
        ans^=tree[x];
        x-=lowbit(x);
    }
    return ans;
}
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;++i){
        scanf("%d",&a[i]);
        sum1[i]=sum1[i-1]^a[i];
    }
    scanf("%d",&m);
    for(int i=1;i<=m;++i){
        scanf("%d%d",&qj[i].l,&qj[i].r);
        qj[i].num=i;
    }
    sort(qj+1,qj+m+1,cmp);
    int r = 1;
    for(int i=1;i<=m;++i){
        while (r <= qj[i].r){
            add(r, a[r]);//我们记录的是异或和 
            if (fl.find(a[r]) != fl.end()){//这个题的数据很大，所以要用map 
                add(fl[a[r]], a[r]);//逆运算还是异或 
            }
            fl[a[r]] = r;
            r++;
        }
        ans[qj[i].num] =sum1[qj[i].r]^sum1[qj[i].l-1]^sum(qj[i].r) ^ sum(qj[i].l - 1);
    }
    for (int i = 1; i <= m; i++) printf("%d\n", ans[i]);
    return 0;
}