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:warning: seq/sidon_sequence.hpp

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Code

#include "mod/mod_sqrt.hpp"
#include "nt/primetest.hpp"
#include "mod/primitive_root.hpp"

// a[i]+a[j] が distinct になるように a[i] を作る
// [0,p(p-1)) に p-1 個という簡単な方法がある.
struct Sidon_Sequence {
  u32 N, p, r;
  // positive にした
  vc<u32> exp, log;
  vc<u64> A;

  Sidon_Sequence(u32 N) : N(N) {
    p = max<ll>(3, N + 1);
    while (!primetest(p)) ++p;
    exp.resize(p - 1);
    log.resize(p);
    u32 r = primitive_root(p);
    exp[0] = 1;
    FOR(i, p - 2) exp[i + 1] = exp[i] * u64(r) % p;
    FOR(i, p - 1) log[exp[i]] = i;
    A.resize(N);
    for (u32 i = 0; i < N; ++i) {
      u64 a = i;
      u64 b = exp[i];
      u64 t = (a < b ? a - b + p - 1 : a - b);
      A[i] = (b + t * p) % (u64(p) * (p - 1));
    }
  }

  u64 operator[](int i) { return A[i]; }

  pair<int, int> query(u64 val) {
    u64 prod = exp[val % (p - 1)];
    u64 sm = val % p;
    u64 sq = (sm * sm + 4 * (p - prod)) % p;
    if (log[sq] & 1) return {-1, -1};
    assert(log[sq] % 2 == 0);
    u64 k = log[sq] / 2;
    u32 x = sm + exp[k], y = sm + p - exp[k];
    x += (x & 1) * p, y += (y & 1) * p;
    x = x / 2 % p, y = y / 2 % p;
    x = log[x], y = log[y];
    if (x < N && y < N && A[x] + A[y] == val) return {x, y};
    return {-1, -1};
  }
};
#line 2 "random/base.hpp"

u64 RNG_64() {
  static u64 x_ = u64(chrono::duration_cast<chrono::nanoseconds>(chrono::high_resolution_clock::now().time_since_epoch()).count()) * 10150724397891781847ULL;
  x_ ^= x_ << 7;
  return x_ ^= x_ >> 9;
}

u64 RNG(u64 lim) { return RNG_64() % lim; }

ll RNG(ll l, ll r) { return l + RNG_64() % (r - l); }
#line 2 "mod/mod_pow.hpp"

#line 2 "mod/mongomery_modint.hpp"

// odd mod.
// x の代わりに rx を持つ
template <int id, typename U1, typename U2>
struct Mongomery_modint {
  using mint = Mongomery_modint;
  inline static U1 m, r, n2;
  static constexpr int W = numeric_limits<U1>::digits;

  static void set_mod(U1 mod) {
    assert(mod & 1 && mod <= U1(1) << (W - 2));
    m = mod, n2 = -U2(m) % m, r = m;
    FOR(5) r *= 2 - m * r;
    r = -r;
    assert(r * m == U1(-1));
  }
  static U1 reduce(U2 b) { return (b + U2(U1(b) * r) * m) >> W; }

  U1 x;
  Mongomery_modint() : x(0) {}
  Mongomery_modint(U1 x) : x(reduce(U2(x) * n2)){};
  U1 val() const {
    U1 y = reduce(x);
    return y >= m ? y - m : y;
  }
  mint &operator+=(mint y) {
    x = ((x += y.x) >= m ? x - m : x);
    return *this;
  }
  mint &operator-=(mint y) {
    x -= (x >= y.x ? y.x : y.x - m);
    return *this;
  }
  mint &operator*=(mint y) {
    x = reduce(U2(x) * y.x);
    return *this;
  }
  mint operator+(mint y) const { return mint(*this) += y; }
  mint operator-(mint y) const { return mint(*this) -= y; }
  mint operator*(mint y) const { return mint(*this) *= y; }
  bool operator==(mint y) const {
    return (x >= m ? x - m : x) == (y.x >= m ? y.x - m : y.x);
  }
  bool operator!=(mint y) const { return not operator==(y); }
  mint pow(ll n) const {
    assert(n >= 0);
    mint y = 1, z = *this;
    for (; n; n >>= 1, z *= z)
      if (n & 1) y *= z;
    return y;
  }
};

template <int id>
using Mongomery_modint_32 = Mongomery_modint<id, u32, u64>;
template <int id>
using Mongomery_modint_64 = Mongomery_modint<id, u64, u128>;
#line 2 "mod/barrett.hpp"

// https://github.com/atcoder/ac-library/blob/master/atcoder/internal_math.hpp
struct Barrett {
  u32 m;
  u64 im;
  explicit Barrett(u32 m = 1) : m(m), im(u64(-1) / m + 1) {}
  u32 umod() const { return m; }
  u32 modulo(u64 z) {
    if (m == 1) return 0;
    u64 x = (u64)(((unsigned __int128)(z)*im) >> 64);
    u64 y = x * m;
    return (z - y + (z < y ? m : 0));
  }
  u64 floor(u64 z) {
    if (m == 1) return z;
    u64 x = (u64)(((unsigned __int128)(z)*im) >> 64);
    u64 y = x * m;
    return (z < y ? x - 1 : x);
  }
  pair<u64, u32> divmod(u64 z) {
    if (m == 1) return {z, 0};
    u64 x = (u64)(((unsigned __int128)(z)*im) >> 64);
    u64 y = x * m;
    if (z < y) return {x - 1, z - y + m};
    return {x, z - y};
  }
  u32 mul(u32 a, u32 b) { return modulo(u64(a) * b); }
};

struct Barrett_64 {
  u128 mod, mh, ml;

  explicit Barrett_64(u64 mod = 1) : mod(mod) {
    u128 m = u128(-1) / mod;
    if (m * mod + mod == u128(0)) ++m;
    mh = m >> 64;
    ml = m & u64(-1);
  }

  u64 umod() const { return mod; }

  u64 modulo(u128 x) {
    u128 z = (x & u64(-1)) * ml;
    z = (x & u64(-1)) * mh + (x >> 64) * ml + (z >> 64);
    z = (x >> 64) * mh + (z >> 64);
    x -= z * mod;
    return x < mod ? x : x - mod;
  }

  u64 mul(u64 a, u64 b) { return modulo(u128(a) * b); }
};
#line 5 "mod/mod_pow.hpp"

u32 mod_pow(int a, ll n, int mod) {
  assert(n >= 0);
  if (mod == 1) return 0;
  a = ((a %= mod) < 0 ? a + mod : a);
  if ((mod & 1) && (mod < (1 << 30))) {
    using mint = Mongomery_modint_32<202311021>;
    mint::set_mod(mod);
    return mint(a).pow(n).val();
  }
  Barrett bt(mod);
  int r = 1;
  while (n) {
    if (n & 1) r = bt.mul(r, a);
    a = bt.mul(a, a), n >>= 1;
  }
  return r;
}

u64 mod_pow_64(ll a, ll n, u64 mod) {
  assert(n >= 0);
  if (mod == 1) return 0;
  a = ((a %= mod) < 0 ? a + mod : a);
  if ((mod & 1) && (mod < (u64(1) << 62))) {
    using mint = Mongomery_modint_64<202311021>;
    mint::set_mod(mod);
    return mint(a).pow(n).val();
  }
  Barrett_64 bt(mod);
  ll r = 1;
  while (n) {
    if (n & 1) r = bt.mul(r, a);
    a = bt.mul(a, a), n >>= 1;
  }
  return r;
}
#line 3 "mod/mod_sqrt.hpp"

// p は素数. 解なしは -1.

int mod_sqrt(int a, int p) {
  if (p == 2) return a;
  if (a == 0) return 0;
  int k = (p - 1) / 2;
  if (mod_pow(a, k, p) != 1) return -1;
  auto find = [&]() -> pi {
    while (1) {
      ll b = RNG(2, p);
      ll D = (b * b - a) % p;
      if (D == 0) return {b, D};
      if (mod_pow(D, k, p) != 1) return {b, D};
    }
  };
  auto [b, D] = find();
  if (D == 0) return b;
  ++k;
  // (b + sqrt(D))^k

  ll f0 = b, f1 = 1, g0 = 1, g1 = 0;
  while (k) {
    if (k & 1) {
      tie(g0, g1) = mp(f0 * g0 + D * f1 % p * g1, f1 * g0 + f0 * g1);
      g0 %= p, g1 %= p;
    }
    tie(f0, f1) = mp(f0 * f0 + D * f1 % p * f1, 2 * f0 * f1);
    f0 %= p, f1 %= p;
    k >>= 1;
  }
  if (g0 < 0) g0 += p;
  return g0;
}

// p は素数. 解なしは -1.

ll mod_sqrt_64(ll a, ll p) {
  if (p == 2) return a;
  if (a == 0) return 0;
  ll k = (p - 1) / 2;
  if (mod_pow_64(a, k, p) != 1) return -1;
  auto find = [&]() -> pair<i128, i128> {
    while (1) {
      i128 b = RNG(2, p);
      i128 D = b * b - a;
      if (D == 0) return {b, D};
      if (mod_pow_64(D, k, p) != 1) return {b, D};
    }
  };
  auto [b, D] = find();
  if (D == 0) return b;
  ++k;
  // (b + sqrt(D))^k

  i128 f0 = b, f1 = 1, g0 = 1, g1 = 0;
  while (k) {
    if (k & 1) {
      tie(g0, g1) = mp(f0 * g0 + D * f1 % p * g1, f1 * g0 + f0 * g1);
      g0 %= p, g1 %= p;
    }
    tie(f0, f1) = mp(f0 * f0 + D * f1 % p * f1, 2 * f0 * f1);
    f0 %= p, f1 %= p;
    k >>= 1;
  }
  return g0;
}
#line 3 "nt/primetest.hpp"

bool primetest(const u64 x) {
  assert(x < u64(1) << 62);
  if (x == 2 or x == 3 or x == 5 or x == 7) return true;
  if (x % 2 == 0 or x % 3 == 0 or x % 5 == 0 or x % 7 == 0) return false;
  if (x < 121) return x > 1;
  const u64 d = (x - 1) >> lowbit(x - 1);

  using mint = Mongomery_modint_64<202311020>;

  mint::set_mod(x);
  const mint one(u64(1)), minus_one(x - 1);
  auto ok = [&](u64 a) -> bool {
    auto y = mint(a).pow(d);
    u64 t = d;
    while (y != one && y != minus_one && t != x - 1) y *= y, t <<= 1;
    if (y != minus_one && t % 2 == 0) return false;
    return true;
  };
  if (x < (u64(1) << 32)) {
    for (u64 a: {2, 7, 61})
      if (!ok(a)) return false;
  } else {
    for (u64 a: {2, 325, 9375, 28178, 450775, 9780504, 1795265022}) {
      if (!ok(a)) return false;
    }
  }
  return true;
}
#line 2 "mod/primitive_root.hpp"

#line 2 "nt/factor.hpp"

#line 5 "nt/factor.hpp"

template <typename mint>
ll rho(ll n, ll c) {
  assert(n > 1);
  const mint cc(c);
  auto f = [&](mint x) { return x * x + cc; };
  mint x = 1, y = 2, z = 1, q = 1;
  ll g = 1;
  const ll m = 1LL << (__lg(n) / 5);
  for (ll r = 1; g == 1; r <<= 1) {
    x = y;
    FOR(r) y = f(y);
    for (ll k = 0; k < r && g == 1; k += m) {
      z = y;
      FOR(min(m, r - k)) y = f(y), q *= x - y;
      g = gcd(q.val(), n);
    }
  }
  if (g == n) do {
      z = f(z);
      g = gcd((x - z).val(), n);
    } while (g == 1);
  return g;
}

ll find_prime_factor(ll n) {
  assert(n > 1);
  if (primetest(n)) return n;
  FOR(100) {
    ll m = 0;
    if (n < (1 << 30)) {
      using mint = Mongomery_modint_32<20231025>;
      mint::set_mod(n);
      m = rho<mint>(n, RNG(0, n));
    } else {
      using mint = Mongomery_modint_64<20231025>;
      mint::set_mod(n);
      m = rho<mint>(n, RNG(0, n));
    }
    if (primetest(m)) return m;
    n = m;
  }
  assert(0);
  return -1;
}

// ソートしてくれる
vc<pair<ll, int>> factor(ll n) {
  assert(n >= 1);
  vc<pair<ll, int>> pf;
  FOR(p, 2, 100) {
    if (p * p > n) break;
    if (n % p == 0) {
      ll e = 0;
      do { n /= p, e += 1; } while (n % p == 0);
      pf.eb(p, e);
    }
  }
  while (n > 1) {
    ll p = find_prime_factor(n);
    ll e = 0;
    do { n /= p, e += 1; } while (n % p == 0);
    pf.eb(p, e);
  }
  sort(all(pf));
  return pf;
}

vc<pair<ll, int>> factor_by_lpf(ll n, vc<int>& lpf) {
  vc<pair<ll, int>> res;
  while (n > 1) {
    int p = lpf[n];
    int e = 0;
    while (n % p == 0) {
      n /= p;
      ++e;
    }
    res.eb(p, e);
  }
  return res;
}
#line 6 "mod/primitive_root.hpp"

// int

int primitive_root(int p) {
  auto pf = factor(p - 1);
  auto is_ok = [&](int g) -> bool {
    for (auto&& [q, e]: pf)
      if (mod_pow(g, (p - 1) / q, p) == 1) return false;
    return true;
  };
  while (1) {
    int x = RNG(1, p);
    if (is_ok(x)) return x;
  }
  return -1;
}

ll primitive_root_64(ll p) {
  auto pf = factor(p - 1);
  auto is_ok = [&](ll g) -> bool {
    for (auto&& [q, e]: pf)
      if (mod_pow_64(g, (p - 1) / q, p) == 1) return false;
    return true;
  };
  while (1) {
    ll x = RNG(1, p);
    if (is_ok(x)) return x;
  }
  return -1;
}

// https://codeforces.com/contest/1190/problem/F

ll primitive_root_prime_power_64(ll p, ll e) {
  assert(p >= 3);
  ll g = primitive_root_64(p);
  ll q = p;
  ll phi = p - 1;
  FOR(e - 1) {
    q *= p;
    phi *= p;
    if (mod_pow_64(g, phi / p, q) == 1) g += q / p;
  }
  return g;
}
#line 4 "seq/sidon_sequence.hpp"

// a[i]+a[j] が distinct になるように a[i] を作る
// [0,p(p-1)) に p-1 個という簡単な方法がある.
struct Sidon_Sequence {
  u32 N, p, r;
  // positive にした
  vc<u32> exp, log;
  vc<u64> A;

  Sidon_Sequence(u32 N) : N(N) {
    p = max<ll>(3, N + 1);
    while (!primetest(p)) ++p;
    exp.resize(p - 1);
    log.resize(p);
    u32 r = primitive_root(p);
    exp[0] = 1;
    FOR(i, p - 2) exp[i + 1] = exp[i] * u64(r) % p;
    FOR(i, p - 1) log[exp[i]] = i;
    A.resize(N);
    for (u32 i = 0; i < N; ++i) {
      u64 a = i;
      u64 b = exp[i];
      u64 t = (a < b ? a - b + p - 1 : a - b);
      A[i] = (b + t * p) % (u64(p) * (p - 1));
    }
  }

  u64 operator[](int i) { return A[i]; }

  pair<int, int> query(u64 val) {
    u64 prod = exp[val % (p - 1)];
    u64 sm = val % p;
    u64 sq = (sm * sm + 4 * (p - prod)) % p;
    if (log[sq] & 1) return {-1, -1};
    assert(log[sq] % 2 == 0);
    u64 k = log[sq] / 2;
    u32 x = sm + exp[k], y = sm + p - exp[k];
    x += (x & 1) * p, y += (y & 1) * p;
    x = x / 2 % p, y = y / 2 % p;
    x = log[x], y = log[y];
    if (x < N && y < N && A[x] + A[y] == val) return {x, y};
    return {-1, -1};
  }
};
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