Sparse Table (RMQ)

#include <bits/stdc++.h>
#define ll long long
#define SaveTime ios_base::sync_with_stdio(false), cin.tie(0);
using namespace std;

const int N = 3e5+7;
const int LOG = 20;
ll Sp[N][LOG];
ll a[N];
int n;

void build() {
   for (int i = 0; i < n; i++)
      Sp[i][0] = a[i];
   for (int j = 1; j < LOG; j++) {
      for (int i = 0; i+ (1<<j)-1 < n; i++) {
         Sp[i][j] = min(Sp[i][j-1], Sp[i+(1<<(j-1))][j-1]);
      }
   }
}

ll get(int qs, int qe) {
   int len = qe-qs+1;
   int k = 0;
   while (1 << (k+1) <= len)
      k++;
   return min(Sp[qs][k], Sp[qe-(1<<k)+1][k]);
}

int main()
{
   SaveTime
   cin >> n;
   for (int i = 0; i < n; i++)
      cin >> a[i];
   build();
}

Resources :
https://youtu.be/0jWeUdxrGm4
Problems :
https://codeforces.com/contest/1549/problem/D