Given an integer n, return the count of prime numbers that are strictly less than n.

Constraints:

• $0 \leq$ n $\leq 5 \times 10^6$

The optimal approach to count all prime numbers strictly less than n uses the Sieve of Eratosthenes, a classic number theory algorithm. The core idea is to initialize every number from $0$ to $n-1$ as a candidate prime, then iteratively mark the multiples of each discovered prime as composite. After the sieve completes, the count of remaining unmarked positions equals the number of primes less than n. This is far more efficient than checking each number individually for primality.

Now, let’s look at the solution steps below:

1. Handle the edge case where n is less than $2$ by immediately returning ...