数学/連立線形合同式
(test/math/simultaneous_linear_congruence.test.cpp)

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• Last update: 2023-02-25 01:48:23+09:00
• Problem: https://yukicoder.me/problems/no/186

Depends on

• 逆元 (inverse element) (include/emthrm/math/mod_inv.hpp)
• 連立線形合同式 (simultaneous linear congruence) (include/emthrm/math/simultaneous_linear_congruence.hpp)

Code

/*
 * @title 数学/連立線形合同式
 *
 * verification-helper: PROBLEM https://yukicoder.me/problems/no/186
 */

#include <iostream>
#include <vector>

#include "emthrm/math/simultaneous_linear_congruence.hpp"

int main() {
  constexpr int N = 3;
  std::vector<long long> x(N), y(N);
  for (int i = 0; i < N; ++i) {
    std::cin >> x[i] >> y[i];
  }
  const auto [ans, mod] = emthrm::simultaneous_linear_congruence(
      std::vector<long long>(N, 1), x, y);
  if (mod == 0) {
    std::cout << "-1\n";
  } else {
    std::cout << (ans == 0 ? mod : ans) << '\n';
  }
  return 0;
}

#line 1 "test/math/simultaneous_linear_congruence.test.cpp"
/*
 * @title 数学/連立線形合同式
 *
 * verification-helper: PROBLEM https://yukicoder.me/problems/no/186
 */

#include <iostream>
#include <vector>

#line 1 "include/emthrm/math/simultaneous_linear_congruence.hpp"



#include <numeric>
#include <utility>
#line 7 "include/emthrm/math/simultaneous_linear_congruence.hpp"

#line 1 "include/emthrm/math/mod_inv.hpp"



#line 6 "include/emthrm/math/mod_inv.hpp"

namespace emthrm {

long long mod_inv(long long a, const int m) {
  if ((a %= m) < 0) a += m;
  if (std::gcd(a, m) != 1) return -1;
  long long x = 1;
  for (long long b = m, u = 0; b > 0;) {
    const long long q = a / b;
    std::swap(a -= q * b, b);
    std::swap(x -= q * u, u);
  }
  x %= m;
  return x < 0 ? x + m : x;
}

}  // namespace emthrm


#line 9 "include/emthrm/math/simultaneous_linear_congruence.hpp"

namespace emthrm {

template <typename T>
std::pair<T, T> simultaneous_linear_congruence(const std::vector<T>& a,
                                               const std::vector<T>& b,
                                               const std::vector<T>& m) {
  const int n = a.size();
  T x = 0, md = 1;
  for (int i = 0; i < n; ++i) {
    const T p = md * a[i], q = -x * a[i] + b[i], g = std::gcd(p, m[i]);
    if (q % g != 0) return {0, -1};
    const T m_i = m[i] / g;
    x += md * (q / g * mod_inv(p / g, m_i) % m_i);
    md *= m_i;
  }
  return {x < 0 ? x + md : x, md};
}

}  // namespace emthrm


#line 11 "test/math/simultaneous_linear_congruence.test.cpp"

int main() {
  constexpr int N = 3;
  std::vector<long long> x(N), y(N);
  for (int i = 0; i < N; ++i) {
    std::cin >> x[i] >> y[i];
  }
  const auto [ans, mod] = emthrm::simultaneous_linear_congruence(
      std::vector<long long>(N, 1), x, y);
  if (mod == 0) {
    std::cout << "-1\n";
  } else {
    std::cout << (ans == 0 ? mod : ans) << '\n';
  }
  return 0;
}

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