RMQ || find the minimum value in specified range

#include <bits/stdc++.h>
#define int long long
using namespace std;
typedef pair<int,int> ii;
typedef vector<ii> vii;
const int N = 100005;

int n,m;
int a[N],f[N][18];

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    freopen("rmq.inp","r",stdin);
    freopen("rmq.out","w",stdout);
    cin >> n >> m;
    for(int i=1; i<=n; ++i)
    {
        cin >> a[i];
    }
    for(int i=1; i<=n; ++i)
    {
        f[i][0] = a[i];
    }
    for(int k=1; (1 << k) <= n; ++k)
        for (int i=1; i+(1<<k)-1 <=n; ++i)
            f[i][k] = min(f[i][k-1],f[i+(1<<(k-1))][k-1]);
    while (m--)
    {
        int l,r;
        cin >> l >> r;
        int k = log2(r-l+1);
        cout << min(f[l][k],f[r-(1<<k)+1][k]) << endl;
    }
    return 0;
}