<p>Given an integer <code>n</code>, return <em>the number of prime numbers that are strictly less than</em> <code>n</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> n = 10
<strong>Output:</strong> 4
<strong>Explanation:</strong> There are 4 prime numbers less than 10, they are 2, 3, 5, 7.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 0
<strong>Output:</strong> 0
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> 0
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>0 &lt;= n &lt;= 5 * 10<sup>6</sup></code></li>
</ul>

import numpy as np

class Solution:
    def countPrimes(self, n: int) -> int:
        
        if n==0 or n==1 or n==2:
            return 0
        
        primes = [True for i in range(n)]
        primes[0] = primes[1] = False
                
        for k in range(2, int(np.sqrt(n))+1):
            if primes[k]:
                for i in range(2, n//k+1):
                    if k*i < len(primes):
                        primes[k*i] = False
        
        return sum(primes)




76468