线段树求问

// luogu-judger-enable-o2
#include<iostream>
#include<algorithm>
#define LS rt<<1,l,mid
#define RS rt<<1|1,mid+1,r
#define PushUp tree[rt].gcd=gcd(tree[rt<<1].gcd,tree[rt<<1|1].gcd)
using namespace std;
const int N=5000000;
int a[N];
int gcd(int a,int b)
{return !b?a:gcd(b,a%b);}
struct Tr{int l,r,gcd;}tree[N];
void build(int rt,int l,int r)
{
    tree[rt].l=l,tree[rt].r=r;
    if(l==r)
    {
        tree[rt].gcd=a[l];
        return;
    }
    int mid=(l+r)>>1;
    build(LS);build(RS);
    PushUp;
}
int find(int rt,int l,int r)
{
    if(l<=tree[rt].l&&r>=tree[rt].r)
        return tree[rt].gcd;
    int mid=(tree[rt].l+tree[rt].r)>>1;
    int r1=0,r2=0;
    if(l<=mid) r1=find(rt<<1,l,r);
    if(r>mid) r2= find(rt<<1|1,l,r);
    //这里要查的区间不变
    if(!r1) tree[rt].gcd=tree[rt<<1|1].gcd;
    if(!r2) tree[rt].gcd=tree[rt<<1].gcd;
    //不存在!r1&&!r2 
    //r=0表示没有if过
    if(r1&&r2) tree[rt].gcd=gcd(r1,r2);
    //·��ѹ��
    return tree[rt].gcd;
}
int n,m;
int main()
{
    ios::sync_with_stdio(false);
    cin>>n>>m;
    for(int i=1;i<=n;++i)cin>>a[i];
    build(1,1,n);
    int x,y;
    while(m--)
    {
        cin>>x>>y;
        cout<<find(1,x,y)<<endl;
    }
    return 0;
}

void build(int rt,int l,int r)
{
    tree[rt].l=l,tree[rt].r=r;
    if(l==r)
    {
        tree[rt].gcd=a[l];
        return;
    }
    int mid=(l+r)>>1;
    build(LS);build(RS);
    PushUp;
}
int find(int rt,int l,int r)
{
    if(l<=tree[rt].l&&r>=tree[rt].r)
        return tree[rt].gcd;
    int mid=(tree[rt].l+tree[rt].r)>>1;
    int r1=0,r2=0;
    if(l<=mid) r1=find(rt<<1,l,r);
    if(r>mid) r2= find(rt<<1|1,l,r);
    //这里要查的区间不变
    if(!r1) tree[rt].gcd=tree[rt<<1|1].gcd;
    if(!r2) tree[rt].gcd=tree[rt<<1].gcd;
    //不存在!r1&&!r2 
    //r=0表示没有if过
    if(r1&&r2) tree[rt].gcd=gcd(r1,r2);
    //自以为是的路径压缩
    return tree[rt].gcd;
}