Problem p02685 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_set>
#include <vector>
#pragma GCC optimize("Ofast")
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int, int>> vpii;
typedef vector<pair<ll, ll>> vpll;
typedef vector<vector<int>> vvi;
typedef vector<vector<char>> vvc;
typedef vector<vector<string>> vvs;
typedef vector<vector<ll>> vvll;
typedef map<int, int> mii;
typedef set<int> si;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define arep(i, v) for (auto i : v)
#define irep(it, stl) for (auto it = stl.begin(); it != stl.end(); it++)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define STLL(s) strtoll(s.c_str(), NULL, 10)
#define mp(p, q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define itn int
// #define endl '\n';
#define fi first
#define se second
#define NONVOID [[nodiscard]]
constexpr int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
constexpr int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
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;
}
template <class T> inline void dump(T &v) {
  irep(i, v) { cout << *i << ((i == --v.end()) ? '\n' : ' '); }
}
inline string getline() {
  string s;
  getline(cin, s);
  return s;
}
inline void yn(const bool b) { b ? fin("yes") : fin("no"); }
inline void Yn(const bool b) { b ? fin("Yes") : fin("No"); }
inline void YN(const bool b) { b ? fin("YES") : fin("NO"); }
struct io {
  io() {
    ios::sync_with_stdio(false);
    cin.tie(0);
  }
};
const int INF = INT_MAX;
constexpr ll LLINF = 1LL << 60;
// constexpr ll MOD = 1000000007;
constexpr double EPS = 1e-9;

int MOD = 998244353;
#define MAX_NCK 101010
ll f[MAX_NCK], rf[MAX_NCK];

// modinvも呼ぶ！！
// (a/b)%P の場合は，(a%P)*modinv(b)%P とする
ll modinv(ll a) {
  ll b = MOD, u = 1, v = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= MOD;
  if (u < 0)
    u += MOD;
  return u;
}
bool isinit = false;

void init(void) {
  f[0] = 1;
  rf[0] = modinv(1);
  for (int i = 1; i < MAX_NCK; i++) {
    f[i] = (f[i - 1] * i) % MOD;
    rf[i] = modinv(f[i]);
  }
}

ll nCk(int n, int k) {
  if (!isinit) {
    init();
    isinit = 1;
  }
  ll nl = f[n];       // n!
  ll nkl = rf[n - k]; // (n-k)!
  ll kl = rf[k];      // k!
  ll nkk = (nkl * kl) % MOD;

  return (nl * nkk) % MOD;
}
// xのn乗%modを計算
ll mod_pow(ll x, ll n, ll mod) {
  ll res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * x % mod;
    x = x * x % mod;
    n >>= 1;
  }
  return res;
}

int main() {

  ll n, m, k;
  cin >> n >> m >> k;
  ll ans = 0;
  for (int i = 0; i <= k; i++) {
    ans += m * mod_pow(m - 1, n - i - 1, MOD) % MOD * nCk(n - 1, i);
    ans %= MOD;
  }
  fin(ans);
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_set>
#include <vector>
#pragma GCC optimize("Ofast")
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int, int>> vpii;
typedef vector<pair<ll, ll>> vpll;
typedef vector<vector<int>> vvi;
typedef vector<vector<char>> vvc;
typedef vector<vector<string>> vvs;
typedef vector<vector<ll>> vvll;
typedef map<int, int> mii;
typedef set<int> si;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define arep(i, v) for (auto i : v)
#define irep(it, stl) for (auto it = stl.begin(); it != stl.end(); it++)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define STLL(s) strtoll(s.c_str(), NULL, 10)
#define mp(p, q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define itn int
// #define endl '\n';
#define fi first
#define se second
#define NONVOID [[nodiscard]]
constexpr int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
constexpr int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
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;
}
template <class T> inline void dump(T &v) {
  irep(i, v) { cout << *i << ((i == --v.end()) ? '\n' : ' '); }
}
inline string getline() {
  string s;
  getline(cin, s);
  return s;
}
inline void yn(const bool b) { b ? fin("yes") : fin("no"); }
inline void Yn(const bool b) { b ? fin("Yes") : fin("No"); }
inline void YN(const bool b) { b ? fin("YES") : fin("NO"); }
struct io {
  io() {
    ios::sync_with_stdio(false);
    cin.tie(0);
  }
};
const int INF = INT_MAX;
constexpr ll LLINF = 1LL << 60;
// constexpr ll MOD = 1000000007;
constexpr double EPS = 1e-9;

int MOD = 998244353;
#define MAX_NCK 201010
ll f[MAX_NCK], rf[MAX_NCK];

// modinvも呼ぶ！！
// (a/b)%P の場合は，(a%P)*modinv(b)%P とする
ll modinv(ll a) {
  ll b = MOD, u = 1, v = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= MOD;
  if (u < 0)
    u += MOD;
  return u;
}
bool isinit = false;

void init(void) {
  f[0] = 1;
  rf[0] = modinv(1);
  for (int i = 1; i < MAX_NCK; i++) {
    f[i] = (f[i - 1] * i) % MOD;
    rf[i] = modinv(f[i]);
  }
}

ll nCk(int n, int k) {
  if (!isinit) {
    init();
    isinit = 1;
  }
  ll nl = f[n];       // n!
  ll nkl = rf[n - k]; // (n-k)!
  ll kl = rf[k];      // k!
  ll nkk = (nkl * kl) % MOD;

  return (nl * nkk) % MOD;
}
// xのn乗%modを計算
ll mod_pow(ll x, ll n, ll mod) {
  ll res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * x % mod;
    x = x * x % mod;
    n >>= 1;
  }
  return res;
}

int main() {

  ll n, m, k;
  cin >> n >> m >> k;
  ll ans = 0;
  for (int i = 0; i <= k; i++) {
    ans += m * mod_pow(m - 1, n - i - 1, MOD) % MOD * nCk(n - 1, i);
    ans %= MOD;
  }
  fin(ans);
}