<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==2:
            return 0
        primes=[True for x_ in range(0,n+1)]

        i=2
        while (i*i<=n):

            if primes[i]==True:
                for x_ in range(i*i,n+1,i):
                    primes[x_]=False
            i+=1
            
        #print(primes)
        return int(np.sum(primes[2:-1]))
            
        #print(primes)
        return int(np.sum(primes[2:]))
118956