eratosfen_n.md

Решето Эратосфена с линейным временем работы

const int N = 10000000;
int lp[N + 1];
vector<int> pr;

for (int i = 2; i <= N; ++i)
{
    if (lp[i] == 0)
    {
        lp[i] = i;
        pr.push_back (i);
    }
    for (int j = 0; j < (int)pr.size() && pr[j] <= lp[i] && i * pr[j] <= N; ++j)
        lp[i * pr[j]] = pr[j];
}

struct SieveOfEratosthenes : std::vector<int>
{
    std::vector<int> primes;
    SieveOfEratosthenes(int MAXN) : std::vector<int>(MAXN + 1) {
        std::iota(begin(), end(), 0);
        for (int i = 2; i <= MAXN; i++) {
            if ((*this)[i] == i) {
                primes.push_back(i);
                for (int j = i; j <= MAXN; j += i) (*this)[j] = i;
            }
        }
    }
    using T = long long int;
    
    std::map<T, int> Factorize(T x) {
        assert(x <= 1LL * (int(size()) - 1) * (int(size()) - 1));
        std::map<T, int> ret;
        if (x < int(size())) {
            while (x > 1) {
                ret[(*this)[x]]++;
                x /= (*this)[x];
            }
        }
        else {
            for (auto p : primes) {
                while (!(x % p)) x /= p, ret[p]++;
                if (x == 1) break;
            }
            if (x > 1) ret[x]++;
        }
        return ret;
    }
    std::vector<T> Divisors(T x) {
        std::vector<T> ret{1};
        for (auto p : Factorize(x)) {
            int n = ret.size();
            for (int i = 0; i < n; i++) {
                for (T a = 1, d = 1; d <= p.second; d++) {
                    a *= p.first;
                    ret.push_back(ret[i] * a);
                }
            }
        }
        return ret; // Not sorted
    }
    
    std::vector<int> GenerateMoebiusFunctionTable() {
        std::vector<int> ret(size());
        for (int i = 1; i < int(size()); i++) {
            if (i == 1) ret[i] = 1;
            else if ((i / (*this)[i]) % (*this)[i] == 0) ret[i] = 0;
            else ret[i] = -ret[i / (*this)[i]];
        }
        return ret;
    }
};
SieveOfEratosthenes sieve(1000000);