<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>

class Solution {
public:
   int prime(int n){
        vector<int> primes;
        if(n<=2) return 0;
        vector<bool>isPrime(n+1, true);
        isPrime[0]=isPrime[1]=true;

        for(long long int i=2; i<=n; i++){
            if(isPrime[i]){
                for(long long int j=i*i; j<=n; j+=i){
                    isPrime[j] = false;
                }
            }
        }
        for(long long int i=2; i<n; i++){
            if(isPrime[i]){
                primes.push_back(i);
            }
        }
        return primes.size();
    }
    int countPrimes(int n) {
        int ans = prime(n);
        return ans;
    }
};
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