Problem p02632 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
using lint = long long;
constexpr lint mod = 1e9 + 7;
#define all(x) (x).begin(), (x).end()
#define bitcount(n) __builtin_popcountl((lint)(n))
#define fcout cout << fixed << setprecision(15)
#define highest(x) (63 - __builtin_clzl(x))
#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rep2(i, l, r) for (int i = int(l); i < int(r); i++)
#define repr(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define repr2(i, l, r) for (int i = int(r) - 1; i >= int(l); i--)
#define SZ(x) int(x.size())
constexpr int inf9 = 1e9;
constexpr lint inf18 = 1e18;
inline void YES(bool condition) {
  if (condition)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
inline void Yes(bool condition) {
  if (condition)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
inline void assertNO(bool condition) {
  if (!condition) {
    cout << "NO" << endl;
    exit(0);
  }
}
inline void assertNo(bool condition) {
  if (!condition) {
    cout << "No" << endl;
    exit(0);
  }
}
inline void assertm1(bool condition) {
  if (!condition) {
    cout << -1 << endl;
    exit(0);
  }
}
lint power(lint base, lint exponent, lint module) {
  if (exponent % 2) {
    return power(base, exponent - 1, module) * base % module;
  } else if (exponent) {
    lint root_ans = power(base, exponent / 2, module);
    return root_ans * root_ans % module;
  } else {
    return 1;
  }
}
struct position {
  int y, x;
};
position mv[4] = {{0, -1}, {1, 0}, {0, 1}, {-1, 0}};
double euclidean(position first, position second) {
  return sqrt((second.x - first.x) * (second.x - first.x) +
              (second.y - first.y) * (second.y - first.y));
}
template <class T, class U> string to_string(pair<T, U> x) {
  return to_string(x.first) + "," + to_string(x.second);
}
string to_string(string x) { return x; }
template <class T> string to_string(complex<T> x) {
  return to_string(make_pair(x.real(), x.imag()));
}
template <class itr> void array_output(itr start, itr goal) {
  string ans;
  for (auto i = start; i != goal; i++)
    cout << (i == start ? "" : " ") << (*i);
  if (!ans.empty())
    ans.pop_back();
  cout << ans << endl;
}
template <class itr> void cins(itr first, itr last) {
  for (auto i = first; i != last; i++) {
    cin >> (*i);
  }
}
template <class T> T gcd(T a, T b) {
  if (b)
    return gcd(b, a % b);
  else
    return a;
}
template <class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
struct combination {
  vector<lint> fact, inv;
  combination(int sz) : fact(sz + 1), inv(sz + 1) {
    fact[0] = 1;
    for (int i = 1; i <= sz; i++) {
      fact[i] = fact[i - 1] * i % mod;
    }
    inv[sz] = power(fact[sz], mod - 2, mod);
    for (int i = sz - 1; i >= 0; i--) {
      inv[i] = inv[i + 1] * (i + 1) % mod;
    }
  }
  lint P(int n, int r) {
    if (r < 0 || n < r)
      return 0;
    return (fact[n] * inv[n - r] % mod);
  }
  lint C(int p, int q) {
    if (q < 0 || p < q)
      return 0;
    return (fact[p] * inv[q] % mod * inv[p - q] % mod);
  }
};
template <class itr> bool next_sequence(itr first, itr last, int max_bound) {
  itr now = last;
  while (now != first) {
    now--;
    (*now)++;
    if ((*now) == max_bound) {
      (*now) = 0;
    } else {
      return true;
    }
  }
  return false;
}
template <class itr, class itr2>
bool next_sequence2(itr first, itr last, itr2 first2, itr2 last2) {
  itr now = last;
  itr2 now2 = last2;
  while (now != first) {
    now--, now2--;
    (*now)++;
    if ((*now) == (*now2)) {
      (*now) = 0;
    } else {
      return true;
    }
  }
  return false;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
inline int at(lint i, int j) { return (i >> j) & 1; }
random_device rnd;
bool is_in_board(lint y, lint x, lint H, lint W) {
  return (0 <= y && y < H && 0 <= x && x < W);
}

// F問題でサンプルの説明文ちょっと見ちゃったけどもう多分解けてるから許して

combination table(1e6 + 1000);

lint get_ans(int k, int s) {
  lint ans = 0, mul = 1;
  rep(i, k + 1) {
    ans += mul * table.C(k + s, i) % mod;
    ans %= mod;
    mul *= 25;
    mul %= mod;
  }
  return ans;
}

int main() {
  int K;
  string S;
  cin >> K >> S;
  cout << get_ans(K, int(S.size())) << endl;

  /*int a = SZ(S), b = SZ(S) + K;
  //int a = 10, b = 10;
  int chars = 26;
  lint dp[a + 1][b + 1];
  rep(i, a + 1){
      dp[i][0] = 0;
  }
  dp[0][0] = 1;
  rep(i, b){
      dp[0][i + 1] = dp[0][i] * chars;
  }
  rep2(i, 1, a + 1){
      rep2(j, 1, b + 1){
          dp[i][j] = (dp[i - 1][j - 1] + dp[i][j - 1] * (chars - 1));
      }
  }
  /*rep(i, a + 1){
      array_output(dp[i] + i, dp[i] + b + 1);
  }
  cout << endl;
  rep(i, a + 1){
      rep2(j, i, b + 1){
          cout << get_ans(i, j) << (j < b ? " " : "\n");
      }
  }
  cout << endl;
  cout << dp[a][b] << endl;*/
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
using lint = long long;
constexpr lint mod = 1e9 + 7;
#define all(x) (x).begin(), (x).end()
#define bitcount(n) __builtin_popcountl((lint)(n))
#define fcout cout << fixed << setprecision(15)
#define highest(x) (63 - __builtin_clzl(x))
#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rep2(i, l, r) for (int i = int(l); i < int(r); i++)
#define repr(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define repr2(i, l, r) for (int i = int(r) - 1; i >= int(l); i--)
#define SZ(x) int(x.size())
constexpr int inf9 = 1e9;
constexpr lint inf18 = 1e18;
inline void YES(bool condition) {
  if (condition)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
inline void Yes(bool condition) {
  if (condition)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
inline void assertNO(bool condition) {
  if (!condition) {
    cout << "NO" << endl;
    exit(0);
  }
}
inline void assertNo(bool condition) {
  if (!condition) {
    cout << "No" << endl;
    exit(0);
  }
}
inline void assertm1(bool condition) {
  if (!condition) {
    cout << -1 << endl;
    exit(0);
  }
}
lint power(lint base, lint exponent, lint module) {
  if (exponent % 2) {
    return power(base, exponent - 1, module) * base % module;
  } else if (exponent) {
    lint root_ans = power(base, exponent / 2, module);
    return root_ans * root_ans % module;
  } else {
    return 1;
  }
}
struct position {
  int y, x;
};
position mv[4] = {{0, -1}, {1, 0}, {0, 1}, {-1, 0}};
double euclidean(position first, position second) {
  return sqrt((second.x - first.x) * (second.x - first.x) +
              (second.y - first.y) * (second.y - first.y));
}
template <class T, class U> string to_string(pair<T, U> x) {
  return to_string(x.first) + "," + to_string(x.second);
}
string to_string(string x) { return x; }
template <class T> string to_string(complex<T> x) {
  return to_string(make_pair(x.real(), x.imag()));
}
template <class itr> void array_output(itr start, itr goal) {
  string ans;
  for (auto i = start; i != goal; i++)
    cout << (i == start ? "" : " ") << (*i);
  if (!ans.empty())
    ans.pop_back();
  cout << ans << endl;
}
template <class itr> void cins(itr first, itr last) {
  for (auto i = first; i != last; i++) {
    cin >> (*i);
  }
}
template <class T> T gcd(T a, T b) {
  if (b)
    return gcd(b, a % b);
  else
    return a;
}
template <class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
struct combination {
  vector<lint> fact, inv;
  combination(int sz) : fact(sz + 1), inv(sz + 1) {
    fact[0] = 1;
    for (int i = 1; i <= sz; i++) {
      fact[i] = fact[i - 1] * i % mod;
    }
    inv[sz] = power(fact[sz], mod - 2, mod);
    for (int i = sz - 1; i >= 0; i--) {
      inv[i] = inv[i + 1] * (i + 1) % mod;
    }
  }
  lint P(int n, int r) {
    if (r < 0 || n < r)
      return 0;
    return (fact[n] * inv[n - r] % mod);
  }
  lint C(int p, int q) {
    if (q < 0 || p < q)
      return 0;
    return (fact[p] * inv[q] % mod * inv[p - q] % mod);
  }
};
template <class itr> bool next_sequence(itr first, itr last, int max_bound) {
  itr now = last;
  while (now != first) {
    now--;
    (*now)++;
    if ((*now) == max_bound) {
      (*now) = 0;
    } else {
      return true;
    }
  }
  return false;
}
template <class itr, class itr2>
bool next_sequence2(itr first, itr last, itr2 first2, itr2 last2) {
  itr now = last;
  itr2 now2 = last2;
  while (now != first) {
    now--, now2--;
    (*now)++;
    if ((*now) == (*now2)) {
      (*now) = 0;
    } else {
      return true;
    }
  }
  return false;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
inline int at(lint i, int j) { return (i >> j) & 1; }
random_device rnd;
bool is_in_board(lint y, lint x, lint H, lint W) {
  return (0 <= y && y < H && 0 <= x && x < W);
}

// F問題でサンプルの説明文ちょっと見ちゃったけどもう多分解けてるから許して

combination table(3e6);

lint get_ans(int k, int s) {
  lint ans = 0, mul = 1;
  rep(i, k + 1) {
    ans += mul * table.C(k + s, i) % mod;
    ans %= mod;
    mul *= 25;
    mul %= mod;
  }
  return ans;
}

int main() {
  int K;
  string S;
  cin >> K >> S;
  cout << get_ans(K, int(S.size())) << endl;

  /*int a = SZ(S), b = SZ(S) + K;
  //int a = 10, b = 10;
  int chars = 26;
  lint dp[a + 1][b + 1];
  rep(i, a + 1){
      dp[i][0] = 0;
  }
  dp[0][0] = 1;
  rep(i, b){
      dp[0][i + 1] = dp[0][i] * chars;
  }
  rep2(i, 1, a + 1){
      rep2(j, 1, b + 1){
          dp[i][j] = (dp[i - 1][j - 1] + dp[i][j - 1] * (chars - 1));
      }
  }
  /*rep(i, a + 1){
      array_output(dp[i] + i, dp[i] + b + 1);
  }
  cout << endl;
  rep(i, a + 1){
      rep2(j, i, b + 1){
          cout << get_ans(i, j) << (j < b ? " " : "\n");
      }
  }
  cout << endl;
  cout << dp[a][b] << endl;*/
}