70分最后几个数据点TLE求大佬指教

#include<bits/stdc++.h>
using namespace std;
const int N=100010;
const int LOG=20;
int n,m;
int a[N];
int st[N][LOG];
int b[N];
inline int read()
{
	int x=0,f_=1;char ch=getchar();
	while (ch<'0'||ch>'9'){if (ch=='-') f_=-1;ch=getchar();}
	while (ch>='0'&&ch<='9'){x=x*10+ch-48;ch=getchar();}
	return x*f_;
}
int main(){
    n=read();
    m=read();
    for(int i=1;i<=n;i++){
        a[i]=read();
    }
    for (int i=2;i<=n;i++){
        b[i]=b[i/2]+1;
    }
    for (int i=1;i<=n;i++){
        st[i][0]=a[i];
    }
    for (int j=1;j<LOG;j++){
        for (int i=1;i+(1<<j)-1<=n;i++){
            st[i][j]=max(st[i][j-1],st[i+(1<<(j-1))][j-1]);
        }
    }
    for (int i=0;i<m;i++){
        int l,r;
        l=read();
        r=read();
        int j=b[r-l+1];
        int ans=max(st[l][j],st[r-(1<<j)+1][j]);
        cout<<ans<<endl;
    }
    return 0;
}