Problem p02715 (C++) — buggy submission, verdict: Runtime Error

#include "bits/stdc++.h"

#define rep(i, a) for (int i = 0; i < (a); ++i)
#define REP(i, a, b) for (int i = (a); i < (b); ++i)
#define vi vector<int>

#define CHOOSE(a) CHOOSE2 a
#define CHOOSE2(a0, a1, a2, a3, a4, x, ...) x
#define debug_1(x1) cerr << #x1 << ": " << x1 << endl
#define debug_2(x1, x2)                                                        \\
  cerr << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << endl
#define debug_3(x1, x2, x3)                                                    \\
  cerr << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": "      \\
       << x3 << endl
#define debug_4(x1, x2, x3, x4)                                                \\
  cerr << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": "      \\
       << x3 << ", " #x4 << ": " << x4 << endl
#define debug_5(x1, x2, x3, x4, x5)                                            \\
  cerr << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": "      \\
       << x3 << ", " #x4 << ": " << x4 << ", " #x5 << ": " << x5 << endl
#define debug(...)                                                             \\
  CHOOSE((__VA_ARGS__, debug_5, debug_4, debug_3, debug_2, debug_1, ~))        \\
  (__VA_ARGS__)

using namespace std;
using ll = long long;
using P = pair<int, int>;

// auto mod int
const int mod = 1000000007;
#pragma GCC diagnostic ignored "-Wshadow"
struct mint {
  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return (*this) *= a.inv(); }
  mint operator/(const mint a) const {
    mint res(*this);
    return res /= a;
  }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }
#pragma GCC diagnostic warning "-Wshadow"

void Main() {
  int n, k;
  cin >> n >> k;
  mint ans = 0;
  vector<mint> d(k + 1, 0);
  for (int i = k; i >= 1; --i) {
    d[i] = mint(k / i).pow(n);
    REP(j, 2, (k / i) + 1) { d[i] -= d[i * j]; }
    ans += d[i] * i;
  }
  cout << ans << endl;
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(15);
  Main();
  return 0;
}


Error: 0

Fixed submission:

#include "bits/stdc++.h"
#include <numeric>

#define rep(i, a) for (int i = 0; i < (a); ++i)
#define REP(i, a, b) for (int i = (a); i < (b); ++i)
#define vi vector<int>

#define CHOOSE(a) CHOOSE2 a
#define CHOOSE2(a0, a1, a2, a3, a4, x, ...) x
#define debug_1(x1) cerr << #x1 << ": " << x1 << endl
#define debug_2(x1, x2)                                                        \\
  cerr << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << endl
#define debug_3(x1, x2, x3)                                                    \\
  cerr << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": "      \\
       << x3 << endl
#define debug_4(x1, x2, x3, x4)                                                \\
  cerr << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": "      \\
       << x3 << ", " #x4 << ": " << x4 << endl
#define debug_5(x1, x2, x3, x4, x5)                                            \\
  cerr << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": "      \\
       << x3 << ", " #x4 << ": " << x4 << ", " #x5 << ": " << x5 << endl
#define debug(...)                                                             \\
  CHOOSE((__VA_ARGS__, debug_5, debug_4, debug_3, debug_2, debug_1, ~))        \\
  (__VA_ARGS__)

using namespace std;
using ll = long long;
using P = pair<int, int>;

// Sieve of Eratosthenes
struct Sieve {
  int n;
  vector<int> f, primes;
  Sieve(int n) : n(n), f(n + 1) {
    f[0] = f[1] = -1;
    for (int i = 2; i <= n; ++i) {
      if (f[i])
        continue;
      primes.emplace_back(i);
      f[i] = i;
      for (int j = i; j <= n; j += i) {
        if (!f[j])
          f[j] = i;
      }
    }
  }

  bool isPrime(int x) { return f[x] == x; }

  vector<int> factorList(int x) {
    vector<int> res;
    while (x != 1) {
      res.push_back(f[x]);
      x /= f[x];
    }
    return res;
  }

  vector<P> factor(int x) {
    vector<int> fl = factorList(x);
    if (fl.size() == 0)
      return {};
    vector<P> res(1, P(fl[0], 0));
    for (int p : fl) {
      if (res.back().first == p)
        res.back().second++;
      else
        res.emplace_back(p, 1);
    }
    return res;
  }
} sieve(100100);

// auto mod int
const int mod = 1000000007;
#pragma GCC diagnostic ignored "-Wshadow"
struct mint {
  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return (*this) *= a.inv(); }
  mint operator/(const mint a) const {
    mint res(*this);
    return res /= a;
  }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }
#pragma GCC diagnostic warning "-Wshadow"

int n, k;
int num = 0;

mint calc(int now, int j, int mode, int mx) {
  mint c = mx / now;
  c = c.pow(n) * mode;
  REP(i, j + 1, num) {
    if (now * sieve.primes[i] > mx)
      break;
    c += calc(now * sieve.primes[i], i, -1 * mode, mx);
  }
  return c;
}

bool yet[100005];
vector<mint> dp;
mint DP(int x) {
  if (yet[x])
    return dp[x];
  while (x >= sieve.primes[num])
    num++;
  yet[x] = true;
  return dp[x] = calc(1, -1, 1, x);
}

void Main() {
  cin >> n >> k;
  vector<int> primes = sieve.primes;
  dp.resize(k);
  mint ans = 0;
  set<int> x;
  for (int i = k; i >= 1; --i) {
    ans += DP(k / i) * mint(i);
    x.insert(k / i);
  }
  cout << ans << endl;
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(15);
  Main();
  return 0;
}