Problem p02982 (C++)

Buggy submission (status: Runtime Error):
// #define NDEBUG
#include <cstddef>
#include <cstdint>
#include <vector>

namespace n91 {

using i8 = std::int_fast8_t;
using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u8 = std::uint_fast8_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

constexpr usize operator"" _z(unsigned long long x) noexcept {
  return static_cast<usize>(x);
}

class rep {
  const usize f, l;

public:
  class itr {
    friend rep;
    usize i;
    constexpr itr(const usize x) noexcept : i(x) {}

  public:
    void operator++() noexcept { ++i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  constexpr rep(const usize first, const usize last) noexcept
      : f(first), l(last) {}
  constexpr itr begin() const noexcept { return itr(f); }
  constexpr itr end() const noexcept { return itr(l); }
};
class revrep {
  const usize f, l;

public:
  class itr {
    friend revrep;
    usize i;
    constexpr itr(usize x) noexcept : i(x) {}

  public:
    void operator++() noexcept { --i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  constexpr revrep(usize first, usize last) noexcept : f(--first), l(--last) {}
  constexpr itr begin() const noexcept { return itr(l); }
  constexpr itr end() const noexcept { return itr(f); }
};
template <class T> using vec_alias = std::vector<T>;
template <class T> auto md_vec(const usize n, const T &value) {
  return std::vector<T>(n, value);
}
template <class... Args> auto md_vec(const usize n, Args... args) {
  return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
}
template <class T> constexpr T difference(const T &a, const T &b) {
  return a < b ? b - a : a - b;
}

} // namespace n91

#include <algorithm>
#include <bitset>
#include <iostream>
#include <numeric>
#include <utility>

namespace n91 {

void main_() {
  std::bitset<1601_z> is_sq;
  for (const auto i : rep(0_z, 41_z)) {
    is_sq.set(i * i);
  }

  usize n, d;
  std::cin >> n >> d;
  auto x = md_vec(n, d, i32());
  for (auto &v : x) {
    for (auto &e : v) {
      std::cin >> e;
    }
  }
  usize cnt = 0_z;
  for (const auto i : rep(0_z, n)) {
    for (const auto j : rep(0_z, i)) {
      i32 sum = static_cast<i32>(0);
      for (const auto k : rep(0_z, d)) {
        sum += (x[i][k] - x[j][k]) * (x[i][k] - x[j][k]);
      }
      if (is_sq.test(static_cast<usize>(sum))) {
        ++cnt;
      }
    }
  }
  std::cout << cnt << std::endl;
}

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Fixed submission:
// #define NDEBUG
#include <cstddef>
#include <cstdint>
#include <vector>

namespace n91 {

using i8 = std::int_fast8_t;
using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u8 = std::uint_fast8_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

constexpr usize operator"" _z(unsigned long long x) noexcept {
  return static_cast<usize>(x);
}

class rep {
  const usize f, l;

public:
  class itr {
    friend rep;
    usize i;
    constexpr itr(const usize x) noexcept : i(x) {}

  public:
    void operator++() noexcept { ++i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  constexpr rep(const usize first, const usize last) noexcept
      : f(first), l(last) {}
  constexpr itr begin() const noexcept { return itr(f); }
  constexpr itr end() const noexcept { return itr(l); }
};
class revrep {
  const usize f, l;

public:
  class itr {
    friend revrep;
    usize i;
    constexpr itr(usize x) noexcept : i(x) {}

  public:
    void operator++() noexcept { --i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  constexpr revrep(usize first, usize last) noexcept : f(--first), l(--last) {}
  constexpr itr begin() const noexcept { return itr(l); }
  constexpr itr end() const noexcept { return itr(f); }
};
template <class T> using vec_alias = std::vector<T>;
template <class T> auto md_vec(const usize n, const T &value) {
  return std::vector<T>(n, value);
}
template <class... Args> auto md_vec(const usize n, Args... args) {
  return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
}
template <class T> constexpr T difference(const T &a, const T &b) {
  return a < b ? b - a : a - b;
}

} // namespace n91

#include <algorithm>
#include <bitset>
#include <iostream>
#include <numeric>
#include <utility>

namespace n91 {

void main_() {
  std::bitset<16001_z> is_sq;
  for (const auto i : rep(0_z, 127_z)) {
    is_sq.set(i * i);
  }

  usize n, d;
  std::cin >> n >> d;
  auto x = md_vec(n, d, i32());
  for (auto &v : x) {
    for (auto &e : v) {
      std::cin >> e;
    }
  }
  usize cnt = 0_z;
  for (const auto i : rep(0_z, n)) {
    for (const auto j : rep(0_z, i)) {
      i32 sum = static_cast<i32>(0);
      for (const auto k : rep(0_z, d)) {
        sum += (x[i][k] - x[j][k]) * (x[i][k] - x[j][k]);
      }
      if (is_sq.test(static_cast<usize>(sum))) {
        ++cnt;
      }
    }
  }
  std::cout << cnt << std::endl;
}

} // namespace n91

int main() {
  n91::main_();
  return 0;
}