O(sqrt(n))

unordered_map<int, int> factors;//存储质因数,first为底数,second为次数

void divide(int x)
{
    for (int i = 2; i <= x / i; i++)
    {
        while (x % i == 0)
        {
            x /= i;
            factors[i]++;
        }
    }
    if (x > 1)
    {
        factors[x]++;
    }
}