Luzhiled's Library

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:heavy_check_mark: Prime Count(素数の個数)
(math/number-theory/prime-count.hpp)

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Code

#include "kth-root-integer.hpp"
#include "prime-table.hpp"

/**
 * @brief Prime Count(素数の個数)
 */
template< int64_t LIM = 100000000000LL >
struct PrimeCount {
private:
  int64_t sq;
  vector< bool > prime;
  vector< int64_t > prime_sum, primes;

  int64_t p2(int64_t x, int64_t y) {
    if(x < 4) return 0;
    int64_t a = pi(y);
    int64_t b = pi(kth_root_integer(x, 2));
    if(a >= b) return 0;
    int64_t sum = (a - 2) * (a + 1) / 2 - (b - 2) * (b + 1) / 2;
    for(int64_t i = a; i < b; i++) sum += pi(x / primes[i]);
    return sum;
  }

  int64_t phi(int64_t m, int64_t n) {
    if(m < 1) return 0;
    if(n > m) return 1;
    if(n < 1) return m;
    if(m <= primes[n - 1] * primes[n - 1]) return pi(m) - n + 1;
    if(m <= primes[n - 1] * primes[n - 1] * primes[n - 1] && m <= sq) {
      int64_t sx = pi(kth_root_integer(m, 2));
      int64_t ans = pi(m) - (sx + n - 2) * (sx - n + 1) / 2;
      for(int64_t i = n; i < sx; ++i) ans += pi(m / primes[i]);
      return ans;
    }
    return phi(m, n - 1) - phi(m / primes[n - 1], n - 1);
  }

public:

  PrimeCount() : sq(kth_root_integer(LIM, 2)), prime_sum(sq + 1) {
    prime = prime_table(sq);
    for(int i = 1; i <= sq; i++) prime_sum[i] = prime_sum[i - 1] + prime[i];
    primes.reserve(prime_sum[sq]);
    for(int i = 1; i <= sq; i++) if(prime[i]) primes.push_back(i);
  }

  int64_t pi(int64_t n) {
    if(n <= sq) return prime_sum[n];
    int64_t m = kth_root_integer(n, 3);
    int64_t a = pi(m);
    return phi(n, a) + a - 1 - p2(n, m);
  }
};
#line 1 "math/number-theory/kth-root-integer.hpp"
uint64_t kth_root_integer(uint64_t a, int k) {
  if(k == 1) return a;
  auto check = [&](uint32_t x) {
    uint64_t mul = 1;
    for(int j = 0; j < k; j++) {
      if(__builtin_mul_overflow(mul, x, &mul)) return false;
    }
    return mul <= a;
  };
  uint64_t ret = 0;
  for(int i = 31; i >= 0; i--) {
    if(check(ret | (1u << i))) ret |= 1u << i;
  }
  return ret;
}
#line 1 "math/number-theory/prime-table.hpp"
/**
 * @brief Prime Table(素数テーブル)
 * @docs docs/prime-table.md
 */
vector< bool > prime_table(int n) {
  vector< bool > prime(n + 1, true);
  if(n >= 0) prime[0] = false;
  if(n >= 1) prime[1] = false;
  for(int i = 2; i * i <= n; i++) {
    if(!prime[i]) continue;
    for(int j = i * i; j <= n; j += i) {
      prime[j] = false;
    }
  }
  return prime;
}
#line 3 "math/number-theory/prime-count.hpp"

/**
 * @brief Prime Count(素数の個数)
 */
template< int64_t LIM = 100000000000LL >
struct PrimeCount {
private:
  int64_t sq;
  vector< bool > prime;
  vector< int64_t > prime_sum, primes;

  int64_t p2(int64_t x, int64_t y) {
    if(x < 4) return 0;
    int64_t a = pi(y);
    int64_t b = pi(kth_root_integer(x, 2));
    if(a >= b) return 0;
    int64_t sum = (a - 2) * (a + 1) / 2 - (b - 2) * (b + 1) / 2;
    for(int64_t i = a; i < b; i++) sum += pi(x / primes[i]);
    return sum;
  }

  int64_t phi(int64_t m, int64_t n) {
    if(m < 1) return 0;
    if(n > m) return 1;
    if(n < 1) return m;
    if(m <= primes[n - 1] * primes[n - 1]) return pi(m) - n + 1;
    if(m <= primes[n - 1] * primes[n - 1] * primes[n - 1] && m <= sq) {
      int64_t sx = pi(kth_root_integer(m, 2));
      int64_t ans = pi(m) - (sx + n - 2) * (sx - n + 1) / 2;
      for(int64_t i = n; i < sx; ++i) ans += pi(m / primes[i]);
      return ans;
    }
    return phi(m, n - 1) - phi(m / primes[n - 1], n - 1);
  }

public:

  PrimeCount() : sq(kth_root_integer(LIM, 2)), prime_sum(sq + 1) {
    prime = prime_table(sq);
    for(int i = 1; i <= sq; i++) prime_sum[i] = prime_sum[i - 1] + prime[i];
    primes.reserve(prime_sum[sq]);
    for(int i = 1; i <= sq; i++) if(prime[i]) primes.push_back(i);
  }

  int64_t pi(int64_t n) {
    if(n <= sq) return prime_sum[n];
    int64_t m = kth_root_integer(n, 3);
    int64_t a = pi(m);
    return phi(n, a) + a - 1 - p2(n, m);
  }
};
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