<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>

# def prime(no):
#     l = len(str(no))
#     t = 0
#     temp = no
#     while no:
#         rem = no % 10
#         t += rem ** l
#         no = int(no / 10)
        
#     if t == temp:
#         return True
#     return False

class Solution:
    def countPrimes(self, n: int) -> int:
        # if n < 3:
        #     return 0

        # out = 0
        # for i in range(2, n):
        #     ot = 1
        #     for j in range(2, i):
        #         if i % j == 0:
        #             ot = 0
        #             break
        #     out += ot
        # return out
    
        arr = [True] * n

        if n == 0 or n == 1:
            return 0

        arr[0], arr[1] = False, False

        for i in range(2, int(n ** 0.5) + 1):
            if arr[i]:
                for j in range(i + i, n, i):
                    arr[j] = False

        return sum(arr)
40418