Count Primes

Description:

Count the number of prime numbers less than a non-negative number, n

click to show more hints.

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

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class Solution
{
public:
int countPrimes(int n)
{
vector<int> a(n);
for(int i=; i<n; i++)
a[i] = i; for(int i=; i * <= n; i++)
{
if(i == )
{
a[i] = ;
continue;
} for(int j = i + i; j < n; j += i)
{
if(a[j] != )
a[j] = ;
}
} int count = ;
for(int i=; i<n; i++)
{
cout << a[i] << " ";
if(a[i] != )
{
count++;
}
}
cout << endl; return count;
}
};

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