bitset sieve

Author: hitonanode

number/bs_sieve.hpp

@@ -0,0 +1,30 @@
+#pragma once
+#include <algorithm>
+#include <bitset>
+#include <cassert>
+#include <vector>
+
+// CUT begin
+// Complexity: O(N log log N):
+// - N = 10^7:  8 /  6 MB,   62 /  81 ms (Codeforces / AtCoder, GCC C++17)
+// - N = 10^8: 61 / 44 MB, 1481 / 866 ms (Codeforces / AtCoder, GCC C++17)
+template <int LIMN> struct BitsetSieve {
+    std::vector<int> primes;
+    std::bitset<LIMN + 1> is_prime;
+    const int maxN;
+    BitsetSieve(int MAXN = LIMN) : maxN(MAXN) {
+        is_prime.set();
+        is_prime.reset(0), is_prime.reset(1);
+        for (int p = 2; p <= MAXN; p++) {
+            if (is_prime[p]) {
+                primes.push_back(p);
+                for (int j = p * 2; j <= MAXN; j += p) is_prime[j] = 0;
+            }
+        }
+    }
+    // Count primes less than or equal to x
+    int prime_counting(int x) {
+        assert(x <= maxN);
+        return std::distance(primes.begin(), std::upper_bound(primes.begin(), primes.end(), x));
+    }
+};

number/test/bs_sieve.test.cpp

@@ -0,0 +1,16 @@
+#define PROBLEM "https://judge.yosupo.jp/problem/enumerate_primes"
+#include "../bs_sieve.hpp"
+#include <iostream>
+#include <vector>
+using namespace std;
+
+int main() {
+    int N, A, B;
+    cin >> N >> A >> B;
+    BitsetSieve<500000001> sieve(N);
+    vector<int> ret;
+    for (unsigned i = 0; A * i + B < sieve.primes.size(); i++) ret.push_back(sieve.primes[A * i + B]);
+    cout << sieve.primes.size() << ' ' << ret.size() << '\n';
+    for (auto p : ret) cout << p << ' ';
+    cout << '\n';
+}