Problem p02632 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
#define rep(i, n) for (ll i = 0; i < n; i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define fi first
#define se second
#define pb push_back
#define debug(x) cerr << #x << ": " << x << endl
#define debug_vec(v)                                                           \\
  cerr << #v << ":";                                                           \\
  rep(i, v.size()) cerr << " " << v[i];                                        \\
  cerr << endl
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
const int INF = (1 << 30) - 1;
const ll LINF = (1LL << 60) - 1;

template <int mod> struct ModInt {
  int x;

  ModInt() : x(0) {}

  ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

  ModInt &operator+=(const ModInt &p) {
    if ((x += p.x) >= mod)
      x -= mod;
    return *this;
  }

  ModInt &operator-=(const ModInt &p) {
    if ((x += mod - p.x) >= mod)
      x -= mod;
    return *this;
  }

  ModInt &operator*=(const ModInt &p) {
    x = (int)(1LL * x * p.x % mod);
    return *this;
  }

  ModInt &operator/=(const ModInt &p) {
    *this *= p.inverse();
    return *this;
  }

  ModInt operator-() const { return ModInt(-x); }

  ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }

  ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }

  ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }

  ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }

  bool operator==(const ModInt &p) const { return x == p.x; }

  bool operator!=(const ModInt &p) const { return x != p.x; }

  ModInt inverse() const {
    int a = x, b = mod, u = 1, v = 0, t;
    while (b > 0) {
      t = a / b;
      swap(a -= t * b, b);
      swap(u -= t * v, v);
    }
    return ModInt(u);
  }

  ModInt pow(int64_t n) const {
    ModInt ret(1), mul(x);
    while (n > 0) {
      if (n & 1)
        ret *= mul;
      mul *= mul;
      n >>= 1;
    }
    return ret;
  }

  friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x; }

  friend istream &operator>>(istream &is, ModInt &a) {
    int64_t t;
    is >> t;
    a = ModInt<mod>(t);
    return (is);
  }

  static int get_mod() { return mod; }
};

const int mod = 1000000007;
using Mint = ModInt<mod>;

template <class T> struct Combination {
  int max_n;
  std::vector<T> f, invf;

  explicit Combination(int n) : max_n(n), f(n + 1), invf(n + 1) {
    f[0] = 1;
    for (int i = 1; i <= n; ++i) {
      f[i] = f[i - 1] * i;
    }

    invf[max_n] = f[max_n].inverse();
    for (int i = max_n - 1; i >= 0; --i) {
      invf[i] = invf[i + 1] * (i + 1);
    }
  }

  T fact(int n) const { return f[n]; }

  T invfact(int n) const { return invf[n]; }

  T perm(int a, int b) const {
    return a < b || b < 0 ? T(0) : f[a] * invf[a - b];
  }

  T comb(int a, int b) const {
    return a < b || b < 0 ? T(0) : f[a] * invf[a - b] * invf[b];
  }
};

Combination<Mint> C(2020202);

void solve() {
  int k;
  string s;
  cin >> k >> s;
  Mint ans = 0;
  rep(i, k + 1) {
    ans += Mint(26).pow(i) * C.comb(s.size() + k - i - 1, s.size() - 1) *
           Mint(25).pow(k - i);
  }
  cout << ans << endl;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
  return 0;
}


Error: 0

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
#define rep(i, n) for (ll i = 0; i < n; i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define fi first
#define se second
#define pb push_back
#define debug(x) cerr << #x << ": " << x << endl
#define debug_vec(v)                                                           \\
  cerr << #v << ":";                                                           \\
  rep(i, v.size()) cerr << " " << v[i];                                        \\
  cerr << endl
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
const int INF = (1 << 30) - 1;
const ll LINF = (1LL << 60) - 1;

template <int mod> struct ModInt {
  int x;

  ModInt() : x(0) {}

  ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

  ModInt &operator+=(const ModInt &p) {
    if ((x += p.x) >= mod)
      x -= mod;
    return *this;
  }

  ModInt &operator-=(const ModInt &p) {
    if ((x += mod - p.x) >= mod)
      x -= mod;
    return *this;
  }

  ModInt &operator*=(const ModInt &p) {
    x = (int)(1LL * x * p.x % mod);
    return *this;
  }

  ModInt &operator/=(const ModInt &p) {
    *this *= p.inverse();
    return *this;
  }

  ModInt operator-() const { return ModInt(-x); }

  ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }

  ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }

  ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }

  ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }

  bool operator==(const ModInt &p) const { return x == p.x; }

  bool operator!=(const ModInt &p) const { return x != p.x; }

  ModInt inverse() const {
    int a = x, b = mod, u = 1, v = 0, t;
    while (b > 0) {
      t = a / b;
      swap(a -= t * b, b);
      swap(u -= t * v, v);
    }
    return ModInt(u);
  }

  ModInt pow(int64_t n) const {
    ModInt ret(1), mul(x);
    while (n > 0) {
      if (n & 1)
        ret *= mul;
      mul *= mul;
      n >>= 1;
    }
    return ret;
  }

  friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x; }

  friend istream &operator>>(istream &is, ModInt &a) {
    int64_t t;
    is >> t;
    a = ModInt<mod>(t);
    return (is);
  }

  static int get_mod() { return mod; }
};

const int mod = 1000000007;
using Mint = ModInt<mod>;

template <typename T> struct Combination {
  vector<T> _fact, _rfact, _inv;

  Combination(int sz) : _fact(sz + 1), _rfact(sz + 1), _inv(sz + 1) {
    _fact[0] = _rfact[sz] = _inv[0] = 1;
    for (int i = 1; i <= sz; i++)
      _fact[i] = _fact[i - 1] * i;
    _rfact[sz] /= _fact[sz];
    for (int i = sz - 1; i >= 0; i--)
      _rfact[i] = _rfact[i + 1] * (i + 1);
    for (int i = 1; i <= sz; i++)
      _inv[i] = _rfact[i] * _fact[i - 1];
  }

  inline T fact(int k) const { return _fact[k]; }

  inline T rfact(int k) const { return _rfact[k]; }

  inline T inv(int k) const { return _inv[k]; }

  T P(int n, int r) const {
    if (r < 0 || n < r)
      return 0;
    return fact(n) * rfact(n - r);
  }

  T C(int p, int q) const {
    if (q < 0 || p < q)
      return 0;
    return fact(p) * rfact(q) * rfact(p - q);
  }

  T H(int n, int r) const {
    if (n < 0 || r < 0)
      return (0);
    return r == 0 ? 1 : C(n + r - 1, r);
  }
};

Combination<Mint> C(1010101);

void solve() {
  int k;
  string s;
  cin >> k >> s;
  Mint ans = 0;
  rep(i, k + 1) {
    ans += Mint(26).pow(i) * C.C(s.size() + k - i - 1, s.size() - 1) *
           Mint(25).pow(k - i);
  }
  cout << ans << endl;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
  return 0;
}