fastsieve.cpp

/* #pragma GCC optimize("O3,unroll-loops") */
/* #pragma GCC optimize("Ofast,unroll-loops") */
/* #pragma GCC target("avx2,popcnt") */
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define pb push_back
#define mp make_pair
#define all(a) begin(a),end(a)
#define FOR(x,val,to) for(int x=(val);x<int((to));++x)
#define FORE(x,val,to) for(auto x=(val);x<=(to);++x)
#define FORR(x,arr) for(auto &x: arr)
#define FORS(x,plus,arr) for(auto x = begin(arr)+(plus); x != end(arr); ++x)
#define FORREV(x,plus,arr) for(auto x = (arr).rbegin()+(plus); x !=(arr).rend(); ++x)
#define REE(s_) {cout<<s_<<'\n';exit(0);}
#define GET(arr) for(auto &i: (arr)) sc(i)
#define whatis(x) cerr << #x << " is " << (x) << endl;
#define debug(x...) cerr << "[" #x "]: ", [](auto... $) {((cerr << $ << "; "), ...); }(x), cerr << '\n'
#define e1 first
#define e2 second
#define INF 0x7f7f7f7f
typedef std::pair<int,int> pi;
typedef std::vector<int> vi;
typedef std::vector<std::string> vs;
typedef int64_t ll;
typedef uint64_t ull;
#define umap unordered_map
#define uset unordered_set
using namespace std;
using namespace __gnu_pbds;
 
#ifdef ONLINE_JUDGE
#define whatis(x) ;
#define debug(x...) ;
#endif
#ifdef _WIN32
#define getchar_unlocked() _getchar_nolock()
#define _CRT_DISABLE_PERFCRIT_LOCKS
#endif
template<class A, class B> auto& operator<<(ostream &o, pair<A, B> p) { return o << '(' << p.first << ", " << p.second << ')'; }
template<class T, enable_if_t<!is_same<T, string>::value, bool> = true> auto operator<<(ostream &o, T x) -> decltype(x.end(), o) { o << '{'; int i = 0; for(auto e : x) o << (", ")+2*!i++ << e; return o << '}'; }
inline void getch(char &x){while(x = getchar_unlocked(), x < 33){;}}
inline void getstr(string &str){str.clear(); char cur;while(cur=getchar_unlocked(),cur<33){;}while(cur>32){str+=cur;cur=getchar_unlocked();}}
template<typename T> inline bool sc(T &num){ bool neg=0; int c; num=0; while(c=getchar_unlocked(),c<33){if(c == EOF) return false;} if(c=='-'){ neg=1; c=getchar_unlocked(); } for(;c>47;c=getchar_unlocked()) num=num*10+c-48; if(neg) num*=-1; return true;}template<typename T, typename ...Args> inline void sc(T &num, Args &...args){ bool neg=0; int c; num=0; while(c=getchar_unlocked(),c<33){;} if(c=='-'){ neg=1; c=getchar_unlocked(); } for(;c>47;c=getchar_unlocked()) num=num*10+c-48; if(neg) num*=-1; sc(args...); }
template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>; //s.find_by_order(), s.order_of_key() <- works like lower_bound
template<typename T> using ordered_map = tree<T, int, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#pragma GCC optimize("O3")
// https://codeforces.com/blog/entry/117775
template <int N = 1'000'000, bool compute_primes = true>
struct fast_sieve {
    std::bitset<N / 3 + 1> sieve;
    vector<int> primes;
    inline bool is_prime(int n) {
        return n == 2 || n == 3 || ((n & 1) && (n % 3) && (sieve[n / 3]));
    }
    void fill_sieve() {
        sieve.set();
        for (int p = 5, d = 4, i = 1, sqn = int(std::sqrt(N)); p <= sqn;
             p += d = 6 - d, i++) {
            if (!sieve[i]) continue;
            for (int q = p * p / 3, r = d * p / 3 + (d * p % 3 == 2), s = 2 * p,
                     qe = (int)sieve.size();
                 q < qe; q += r = s - r)
                sieve[q] = 0;
        }
    }
    vector<int> get_primes() {
        vector<int> ret{2, 3};
        for (int p = 5, d = 4, i = 1; p <= N; p += d = 6 - d, i++)
            if (sieve[i]) ret.push_back(p);
        while (!ret.empty() && ret.back() > N) ret.pop_back();
        return ret;
    }
    fast_sieve() {
        fill_sieve();
        if (compute_primes) primes = get_primes();
    }
};

 
int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);
}