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

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<long long> vll;
typedef vector<pair<int, int>> vpi;
typedef vector<pair<long long, long long>> vpl;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
#define INF (int)(1e9)
#define MAXX 1.1529215e+18
#define inf 999999
#define EPS (1e-7)
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define REP(i, n) for (int i = 1; i <= (int)(n); i++)
#define FOR(i, k, n) for (int i = (k); i < (int)(n); i++)
#define ALL(a) a.begin(), a.end()
#define RALL(a) a.begin(), a.end(), greater<int>()
#define ROT(a) a.begin(), a.begin() + 1, a.end()
#define RROT(a) a.begin(), a.end() - 1, a.end()
#define PB push_back
#define MP make_pair
#define PI acos(-1.0)
#define sz(a) a.size()
ll MOD = 998244353;
ll mod = 998244353;
const int MAX = 10000000;
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T> T gcd(T a, T b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
// cout << 'H' << endl;
/*--------------------------------------------*/

long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void C_init() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}

// 二項係数計算
long long nCr(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

ll modpow(ll x, ll n, ll mod) {
  if (n == 0)
    return 1;
  ll res = modpow(x * x % mod, n / 2, mod);
  if (n & 1)
    res = res * x % mod;
  return res;
}

int main() {
  // cout << fixed << setprecision(10)
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll N, M, K;
  cin >> N >> M >> K;

  C_init();

  ll ans = 0;

  for (int k = 0; k <= K; k++) {
    ans += (((M * nCr(N - 1, k)) % mod) * modpow(M - 1, N - k - 1, mod)) % mod;
    ans %= mod;
  }

  cout << ans << endl;
}


Error: -11

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<long long> vll;
typedef vector<pair<int, int>> vpi;
typedef vector<pair<long long, long long>> vpl;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
#define INF (int)(1e9)
#define MAXX 1.1529215e+18
#define inf 999999
#define EPS (1e-7)
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define REP(i, n) for (int i = 1; i <= (int)(n); i++)
#define FOR(i, k, n) for (int i = (k); i < (int)(n); i++)
#define ALL(a) a.begin(), a.end()
#define RALL(a) a.begin(), a.end(), greater<int>()
#define ROT(a) a.begin(), a.begin() + 1, a.end()
#define RROT(a) a.begin(), a.end() - 1, a.end()
#define PB push_back
#define MP make_pair
#define PI acos(-1.0)
#define sz(a) a.size()
const ll MOD = 1e9 + 7;
const int MAX = 10000000;
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T> T gcd(T a, T b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
// cout << 'H' << endl;
/*--------------------------------------------*/

int N, M, K;
int mod = 998244353;

ll dfs(int x, int k) {
  if (x == 1 && k == 0) {
    return M;
  }

  int tmp = 0;

  tmp += dfs(x - 1, k);
  tmp %= mod;

  if (k >= 1) {
    tmp += (M - 1) * dfs(x - 1, k - 1);
    tmp %= mod;
  }

  return tmp;
}

int main() {
  // cout << fixed << setprecision(10)
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin >> N >> M >> K;

  cout << dfs(N, K) << endl;
}