Problem p02685 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
#define rep2(i, s, n) for (int i = (s); i < (n); ++i)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define pb push_back
#define eb emplace_back
#define vi vector<int>
#define vvi vector<vector<int>>
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vs vector<string>
#define vc vector<char>
#define vb vector<bool>
#define vp vector<P>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using LP = pair<ll, ll>;
template <class T> istream &operator>>(istream &is, vector<T> &v) {
  for (T &t : v) {
    is >> t;
  }
  return is;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (T t : v) {
    os << t << " ";
  }
  os << "\n";
  return os;
}
void Yes(bool b) { cout << (b ? "Yes" : "No") << endl; }
void YES(bool b) { cout << (b ? "YES" : "NO") << endl; }
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
const int inf = 1001001001;
const ll linf = 1001001001001001001;

// const int mod = 1000000007;
const int mod = 998244353;
struct mint {
  ll x;
  explicit 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++() {
    x += 1;
    return *this;
  }
  mint &operator-=(const mint &a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator--() {
    x -= 1;
    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;
  }
  bool operator==(const int &n) const {
    mint a(n);
    return this->x == a.x;
  }
  bool operator==(const ll &n) const {
    mint a(n);
    return this->x == a.x;
  }
  bool operator!=(const int &n) const {
    mint a(n);
    return this->x != a.x;
  }
  bool operator!=(const ll &n) const {
    mint a(n);
    return this->x != a.x;
  }
  mint pow(ll t) const {
    mint res = mint(1), a(*this);
    while (t > 0) {
      if (t & 1)
        res *= a;
      t >>= 1;
      a *= a;
    }
    return res;
  }
  // 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;
  }
};
ostream &operator<<(ostream &os, const mint &m) { return os << m.x; }

class combination {
  vector<mint> fact, ifact;

public:
  combination(int n) : fact(n + 1), ifact(n + 1) {
    assert(n < mod);
    fact[0] = mint(1);
    for (int i = 1; i <= n; ++i)
      fact[i] = fact[i - 1] * mint(i);
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i)
      ifact[i - 1] = ifact[i] * mint(i);
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n)
      return mint(0);
    return fact[n] * ifact[k] * ifact[n - k];
  }
} comb(100010);

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int n, m, k;
  cin >> n >> m >> k;
  mint ans(0);
  rep(i, k + 1) {
    mint nans(1);
    nans *= mint(m - 1).pow(n - i - 1);
    nans *= mint(m);
    nans *= comb(n - 1, i);
    ans += nans;
  }
  cout << ans << endl;
}


Fixed submission:
#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
#define rep2(i, s, n) for (int i = (s); i < (n); ++i)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define pb push_back
#define eb emplace_back
#define vi vector<int>
#define vvi vector<vector<int>>
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vs vector<string>
#define vc vector<char>
#define vb vector<bool>
#define vp vector<P>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using LP = pair<ll, ll>;
template <class T> istream &operator>>(istream &is, vector<T> &v) {
  for (T &t : v) {
    is >> t;
  }
  return is;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (T t : v) {
    os << t << " ";
  }
  os << "\n";
  return os;
}
void Yes(bool b) { cout << (b ? "Yes" : "No") << endl; }
void YES(bool b) { cout << (b ? "YES" : "NO") << endl; }
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
const int inf = 1001001001;
const ll linf = 1001001001001001001;

// const int mod = 1000000007;
const int mod = 998244353;
struct mint {
  ll x;
  explicit 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++() {
    x += 1;
    return *this;
  }
  mint &operator-=(const mint &a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator--() {
    x -= 1;
    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;
  }
  bool operator==(const int &n) const {
    mint a(n);
    return this->x == a.x;
  }
  bool operator==(const ll &n) const {
    mint a(n);
    return this->x == a.x;
  }
  bool operator!=(const int &n) const {
    mint a(n);
    return this->x != a.x;
  }
  bool operator!=(const ll &n) const {
    mint a(n);
    return this->x != a.x;
  }
  mint pow(ll t) const {
    mint res = mint(1), a(*this);
    while (t > 0) {
      if (t & 1)
        res *= a;
      t >>= 1;
      a *= a;
    }
    return res;
  }
  // 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;
  }
};
ostream &operator<<(ostream &os, const mint &m) { return os << m.x; }

class combination {
  vector<mint> fact, ifact;

public:
  combination(int n) : fact(n + 1), ifact(n + 1) {
    assert(n < mod);
    fact[0] = mint(1);
    for (int i = 1; i <= n; ++i)
      fact[i] = fact[i - 1] * mint(i);
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i)
      ifact[i - 1] = ifact[i] * mint(i);
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n)
      return mint(0);
    return fact[n] * ifact[k] * ifact[n - k];
  }
} comb(200010);

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int n, m, k;
  cin >> n >> m >> k;
  mint ans(0);
  rep(i, k + 1) {
    mint nans(1);
    nans *= mint(m - 1).pow(n - i - 1);
    nans *= mint(m);
    nans *= comb(n - 1, i);
    ans += nans;
  }
  cout << ans << endl;
}