$30pts$求助

#include<iostream>
#include<cstdio>
using namespace std;
int n,m,a,power[21],Log[200001],f[21][100001],l,r;
int main()
{
    scanf("%d%d",&n,&m);
    power[0]=1;
    for(int i=1;i<=20;++i)
        power[i]=power[i-1]*2;
    Log[0]=-1;
    for(int i=1;i<=200000;++i)
        Log[i]=Log[i/2]+1;
    for(int i=1;i<=n;++i)
    {
        scanf("%d",&a);
        f[0][i]=a;
    }
    for(int i=1;i<=Log[n];++i)
        for(int j=1;j<=n;++j)
            if(j+power[i]-1<=n)
                f[i][j]=max(f[i-1][j],f[i-1][j+power[i-1]]);
    while(m--)
    {
        scanf("%d%d",&l,&r);
        int k=Log[r-l+1];
        printf("%d\n",max(f[k-1][l],f[k][r-power[k]+1]));
    }
    return 0;
}