为什么 TLE 最后一个点

#include<bits/stdc++.h>
#define int long long
using namespace std;
int n,m,a[1005];
struct node{
	int l,r,gcd;
}tree[4005];
int gcd(int a,int b){
	if(b==0)return a;
	return gcd(b,a%b);
}
void build(int x,int l,int r){
	tree[x].l=l;
	tree[x].r=r;
	if(l==r){
		tree[x].gcd=a[l];
		return;
	}
	int mid=l+r>>1;
	build(x<<1,l,mid);
	build(x<<1|1,mid+1,r);
	tree[x].gcd=gcd(tree[x<<1].gcd,tree[x<<1|1].gcd);
}
int query(int x,int l,int r){
	if(l<=tree[x].l&&tree[x].r<=r)return tree[x].gcd;
	int mid=tree[x].l+tree[x].r>>1,ans=0;
	if(l<=mid)ans=gcd(ans,query(x<<1,l,r));
	if(mid+1<=r)ans=gcd(ans,query(x<<1|1,l,r));
	return ans;
}
signed main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++)cin>>a[i];
	build(1,1,n);
	while(m--){
		int l,r;
		cin>>l>>r;
		cout<<query(1,l,r)<<'\n';
	}
	return 0;
}