Problem p02625 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <vector>
using namespace std;
#define sim template <class c
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                 \\
  sim > typename enable_if<sizeof dud<c>(0) x 1, debug &>::type operator<<(    \\
            c i) {
sim > struct rge {
  c b, e;
};
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c *x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
  ~debug() { cerr << endl; }
  eni(!=) cerr << boolalpha << i;
  ris;
} eni(==) ris << range(begin(i), end(i));
}
sim, class b dor(pair<b, c> d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
  sim dor(const c &) { ris; }
#endif
}
;
#define pp(...) "\\033[94m [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "]\\033[0m"
#define pp1(...)                                                               \\
  "\\033[1;47;35m" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "]\\033[0m"
#define dg(x) debug() << pp1(x)
#define dg1(x) debug() << pp(x)
#define dg2(x, y) debug() << pp(x) pp(y)
#define dg3(x, y, z) debug() << pp(x) pp(y) pp(z)
#define dg4(w, x, y, z) debug() << pp(w) pp(x) pp(y) pp(z)
#define int long long
#define all(x) x.begin(), x.end()
#define clr(x) memset(x, 0, sizeof x);
#define sz(x) (int)x.size()
template <typename T> void db(T x) { debug() << ">>> " << x; }
template <typename T> void db(T x, T y) {
  debug() << ">>> " << x << " , " << y;
}
template <typename T> void db(T x, T y, T z) {
  debug() << ">>> " << x << " , " << y << " , " << z;
}
template <typename T> void db(T x, T y, T z, T a) {
  debug() << ">>> " << x << " , " << y << " , " << z << " , " << a;
}
const int xx = 2e5;
const int Mod = 1e9 + 7;
const int inf = 1e18;
const int Maxn = 20010;

vector<int> fac, facInv, inv;
void facInit(int nmax) {
  fac = facInv = inv = vector<int>(nmax + 1, 1);
  for (int i = 2; i <= nmax; i++) {
    fac[i] = fac[i - 1] * i % Mod;
    inv[i] = Mod - inv[Mod % i] * (Mod / i) % Mod;
    facInv[i] = facInv[i - 1] * inv[i] % Mod;
  }
}

int mul(int a, int b, int c) { return (((a * b) % Mod) * c % Mod) % Mod; }
int C(int n, int r) { return mul(fac[n], facInv[r], facInv[n - r]); }
int P(int n, int r) { return (fac[n] * facInv[n - r]) % Mod; }
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  int N, M;
  cin >> N >> M;
  facInit(M + 1);
  int ans = 0;
  int cur = 1;
  for (int i = 0; i <= N; i++) {
    ans += mul(cur, C(N, i), P(M - i, N - i));
    ans = ans % Mod;
    cur = cur * -1;
    ans = (ans + Mod) % Mod;
  }
  dg1(ans);
  ans = (ans * P(M, N)) % Mod;
  cout << ans << '\\n';
}

Error: 0

Fixed submission:

#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <vector>
using namespace std;
#define sim template <class c
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                 \\
  sim > typename enable_if<sizeof dud<c>(0) x 1, debug &>::type operator<<(    \\
            c i) {
sim > struct rge {
  c b, e;
};
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c *x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
  ~debug() { cerr << endl; }
  eni(!=) cerr << boolalpha << i;
  ris;
} eni(==) ris << range(begin(i), end(i));
}
sim, class b dor(pair<b, c> d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
  sim dor(const c &) { ris; }
#endif
}
;
#define pp(...) "\\033[94m [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "]\\033[0m"
#define pp1(...)                                                               \\
  "\\033[1;47;35m" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "]\\033[0m"
#define dg(x) debug() << pp1(x)
#define dg1(x) debug() << pp(x)
#define dg2(x, y) debug() << pp(x) pp(y)
#define dg3(x, y, z) debug() << pp(x) pp(y) pp(z)
#define dg4(w, x, y, z) debug() << pp(w) pp(x) pp(y) pp(z)
#define int long long
#define all(x) x.begin(), x.end()
#define clr(x) memset(x, 0, sizeof x);
#define sz(x) (int)x.size()
template <typename T> void db(T x) { debug() << ">>> " << x; }
template <typename T> void db(T x, T y) {
  debug() << ">>> " << x << " , " << y;
}
template <typename T> void db(T x, T y, T z) {
  debug() << ">>> " << x << " , " << y << " , " << z;
}
template <typename T> void db(T x, T y, T z, T a) {
  debug() << ">>> " << x << " , " << y << " , " << z << " , " << a;
}
const int xx = 2e5;
const int Mod = 1e9 + 7;
const int inf = 1e18;
const int Maxn = 20010;

vector<int> fac, facInv, inv;
void facInit(int nmax) {
  fac = facInv = inv = vector<int>(nmax + 1, 1);
  for (int i = 2; i <= nmax; i++) {
    fac[i] = fac[i - 1] * i % Mod;
    inv[i] = Mod - inv[Mod % i] * (Mod / i) % Mod;
    facInv[i] = facInv[i - 1] * inv[i] % Mod;
  }
}

int C(int n, int r) {
  return (fac[n] * facInv[r] % Mod * facInv[n - r] % Mod) % Mod;
}
int P(int n, int r) { return (fac[n] * facInv[n - r] % Mod) % Mod; }
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  int N, M;
  cin >> N >> M;
  facInit(N + 1);
  int ans = 0;
  int cur = 1;
  for (int i = 1; i <= N; i++) {
    ans += (cur * C(N, i) % Mod * P(M - i, N - i)) % Mod;
    dg1(ans);
    cur = cur * -1;
    ans = ans + Mod % Mod;
  }
  ans = (ans * P(M, N)) % Mod;
  cout << ans << '\\n';
}