Problem p02685 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>

using namespace std;

typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vii;
typedef vector<ll> vll;
typedef pair<int, int> pii;

#define FASTIO                                                                 \\
  ios::sync_with_stdio(false);                                                 \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
#define pb push_back
#define ff it->first
#define ss it->second
#define all(v) (v).begin(), (v).end()
#define rep(i, n) for (auto i = 0; i < n; ++i)
#define LOOP_IT(it, s) for (auto it = (s).begin(); it != (s).end(); ++it)

#ifdef LOCAL
#define cerr cout
#else
#endif

#define TRACE

#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
#else
#define trace(...)
#endif

void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\\'' << x << '\\''; }
void __print(const char *x) { cerr << '\\"' << x << '\\"'; }
void __print(const string &x) { cerr << '\\"' << x << '\\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }

template <typename T, typename V> void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T> void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x)
    cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\\n"; }
template <typename T, typename... V> void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v))
    cerr << ", ";
  _print(v...);
}
#ifndef ONLINE_JUDGE
#define debug(x...)                                                            \\
  cerr << "[" << #x << "] = [";                                                \\
  _print(x)
#else
#define debug(x...)
#endif

ll const mod = 998244353;

ll f[200001];

ll mod_pow(ll a, ll n) {
  ll res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % mod;
    a = (a * a) % mod;
    n >>= 1;
  }
  return res;
}

ll mod_inv(ll x, ll mod) { return mod_pow(x, mod - 2); }

ll nCr(ll n, ll r) {
  return (f[n] * ((mod_inv(f[r], mod) * mod_inv(f[n - r], mod)) % mod)) % mod;
}

int main(int argv, char *argc[]) {
  FASTIO

  f[0] = 1;
  for (ll i = 1; i <= 200000; i++)
    f[i] = (f[i - 1] * i) % mod;

  ll n, m, k, sum = 0;
  cin >> n >> m >> k;

  for (ll i = 0; i <= k; ++i) {
    ll a = 1;

    a *= m;
    a %= mod;
    a *= mod_pow(m - 1, n - i - 1);
    a %= mod;
    a *= nCr(n - 1, n - i - 1);
    a %= mod;

    sum += a;
    sum %= mod;
  }
  cout << sum;

  return 0;
}


Error: WA

Fixed submission:

#include <bits/stdc++.h>

using namespace std;

typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vii;
typedef vector<ll> vll;
typedef pair<int, int> pii;

#define FASTIO                                                                 \\
  ios::sync_with_stdio(false);                                                 \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
#define pb push_back
#define ff it->first
#define ss it->second
#define all(v) (v).begin(), (v).end()
#define rep(i, n) for (auto i = 0; i < n; ++i)
#define LOOP_IT(it, s) for (auto it = (s).begin(); it != (s).end(); ++it)

#ifdef LOCAL
#define cerr cout
#else
#endif

#define TRACE

#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
#else
#define trace(...)
#endif

void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\\'' << x << '\\''; }
void __print(const char *x) { cerr << '\\"' << x << '\\"'; }
void __print(const string &x) { cerr << '\\"' << x << '\\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }

template <typename T, typename V> void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T> void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x)
    cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\\n"; }
template <typename T, typename... V> void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v))
    cerr << ", ";
  _print(v...);
}
#ifndef ONLINE_JUDGE
#define debug(x...)                                                            \\
  cerr << "[" << #x << "] = [";                                                \\
  _print(x)
#else
#define debug(x...)
#endif

ll const mod = 998244353;

ll f[100001];

ll mod_pow(ll a, ll n) {
  ll res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % mod;
    a = (a * a) % mod;
    n >>= 1;
  }
  return res;
}

ll mod_inv(ll x, ll mod) { return mod_pow(x, mod - 2); }

ll nCr(ll n, ll r) {
  return (f[n] * ((mod_inv(f[r], mod) * mod_inv(f[n - r], mod)) % mod)) % mod;
}

int main(int argv, char *argc[]) {
  FASTIO

  f[0] = 1;
  for (ll i = 1; i <= 100000; i++)
    f[i] = (f[i - 1] * i) % mod;

  ll n, m, k, sum = 0;
  cin >> n >> m >> k;

  for (ll i = 0; i <= k; ++i) {
    ll a = 1;

    a *= m;
    a %= mod;
    a *= mod_pow(m - 1, n - i - 1);
    a %= mod;
    a *= nCr(n - 1, n - i - 1);
    a %= mod;

    sum += a;
    sum %= mod;
  }
  cout << sum;

  return 0;
}