Problem p03013 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
#define pa pair<int, int>
#define pal pair<long long, long long>
#define pali pair<long long, int>
#define pad pair<double, double>
#define pb push_back
#define mp make_pair
#define COUT(v)                                                                \
  for (int64_t i = 0; i < (v).size(); ++i) {                                   \
    cout << v.at(i) << endl;                                                   \
  }
#define REP(i, n) for (int64_t i = 0; i < n; ++i)
#define FOR(i, r, n) for (int64_t i = (r); i < n; ++i)
#define VIN(v)                                                                 \
  for (int64_t i = 0; i < (v).size(); ++i) {                                   \
    cin >> (v).at(i);                                                          \
  }

typedef vector<bool> bvec;
typedef vector<int> ivec;
typedef vector<long long> lvec;
typedef vector<double> dvec;
typedef vector<pa> pavec;
typedef vector<pali> palivec;
typedef vector<pal> palvec;

typedef vector<vector<bool>> bmat;
typedef vector<vector<int>> imat;
typedef vector<vector<long long>> lmat;

typedef vector<string> svec;
typedef vector<vector<string>> smat;
const ll infll = (1LL << 60) - 1;
const int inf = (1 << 30) - 1;
const ll MOD = 1000000007;

ll gcd(ll x, ll y) {
  ll r = x % y;
  if (r == 0)
    return y;
  else
    return gcd(y, r);
}

ll lcm(ll x, ll y) { return x * y / gcd(x, y); }

lvec mfactor(ll n) {
  bvec ip(n, true);
  lvec mf(n, -1);
  ip[0] = false;
  ip[1] = false;
  mf[0] = 0;
  mf[1] = 1;
  REP(i, n) {
    if (ip[i]) {
      mf[i] = i;
      for (ll j = i * i; j < n; j += i) {
        ip[j] = false;
        if (mf[j] == -1)
          mf[j] = i;
      }
    }
  }
  return mf;
}

palivec get_prime(ll n, const lvec &mf) {
  palivec plist;
  while (n != 1) {
    int cnt = 0;
    ll m = mf[n];
    while (mf[n] == m) {
      cnt++;
      n /= m;
    }
    plist.pb(pali(m, cnt));
  }
  return plist;
}

void COMinit(int m, lvec &fac, lvec &finv) {
  lvec inv(m);
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < m; 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;
  }
}

ll pow_mod(ll a, ll n) {
  ll x = 1;
  while (n > 0) {
    if (n & 1) {
      x = x * a % MOD;
    }
    a = a * a % MOD;
    n >>= 1;
  }
  return x;
}

ll COM(int n, int k, const lvec &fac, const lvec &finv) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

ll modinv(ll a, ll m) {
  ll b = m, u = 1, v = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}

ll P(ll n, ll m) {
  ll s = 1;
  ll cnt = n;
  REP(i, n - m) {
    s *= cnt % MOD;
    s %= MOD;
    --cnt;
  }
  return s;
}

void fac(int a, int b, bvec &fmap) {
  for (int i = 2; i < b; i++) {
    if (fmap[i])
      continue;
    else if (a % i == 0) {
      fmap[i] = true;
      int n = a / i, x = i;
      while (n >= i) {
        n /= i;
        x += i;
        fmap[x] = true;
      }
    }
  }
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  ivec a(m + 1);
  for (int i = 0; i < m; i++) {
    cin >> a[i];
  }
  a[m] = n + 1;
  lvec dp(n);
  dp[0] = 1;
  dp[1] = 1;
  for (int i = 2; i < n + 1; i++) {
    dp[i] = dp[i - 1] + dp[i - 2];
    dp[i] %= MOD;
  }
  ll ans = 1;
  int c = 0;
  for (int i = 0; i < m + 1; i++) {
    int ns = a[i] - c - 1;
    if (ns < 0) {
      cout << 0 << endl;
      return 0;
    }
    ans *= dp[ns];
    ans %= MOD;
    c = a[i] + 1;
  }

  /*
  lvec fac(n+1), finv(n+1);
  COMinit(n+1, fac, finv);
  int c=0;
  ll ans=1;
  for (int i=0; i<m+1; i++){
      int ns = a[i]-c-1;
      if(ns<0) {
          cout << 0 << endl;
          return 0;
      }
      int n2=0;
      int nss = ns;
      ll tmp=0;
      while(((nss >= n2)&&!(ns%2)) || ((nss > n2)&&(ns%2))){
          //cout << nss << ' ' << n2 << endl;
          tmp+=COM(nss, n2, fac, finv);
          ++n2;
          --nss;
      }
      ans*=tmp;
      ans%=MOD;
      c = a[i]+1;
  }
  */
  cout << ans << endl;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
#define pa pair<int, int>
#define pal pair<long long, long long>
#define pali pair<long long, int>
#define pad pair<double, double>
#define pb push_back
#define mp make_pair
#define COUT(v)                                                                \
  for (int64_t i = 0; i < (v).size(); ++i) {                                   \
    cout << v.at(i) << endl;                                                   \
  }
#define REP(i, n) for (int64_t i = 0; i < n; ++i)
#define FOR(i, r, n) for (int64_t i = (r); i < n; ++i)
#define VIN(v)                                                                 \
  for (int64_t i = 0; i < (v).size(); ++i) {                                   \
    cin >> (v).at(i);                                                          \
  }

typedef vector<bool> bvec;
typedef vector<int> ivec;
typedef vector<long long> lvec;
typedef vector<double> dvec;
typedef vector<pa> pavec;
typedef vector<pali> palivec;
typedef vector<pal> palvec;

typedef vector<vector<bool>> bmat;
typedef vector<vector<int>> imat;
typedef vector<vector<long long>> lmat;

typedef vector<string> svec;
typedef vector<vector<string>> smat;
const ll infll = (1LL << 60) - 1;
const int inf = (1 << 30) - 1;
const ll MOD = 1000000007;

ll gcd(ll x, ll y) {
  ll r = x % y;
  if (r == 0)
    return y;
  else
    return gcd(y, r);
}

ll lcm(ll x, ll y) { return x * y / gcd(x, y); }

lvec mfactor(ll n) {
  bvec ip(n, true);
  lvec mf(n, -1);
  ip[0] = false;
  ip[1] = false;
  mf[0] = 0;
  mf[1] = 1;
  REP(i, n) {
    if (ip[i]) {
      mf[i] = i;
      for (ll j = i * i; j < n; j += i) {
        ip[j] = false;
        if (mf[j] == -1)
          mf[j] = i;
      }
    }
  }
  return mf;
}

palivec get_prime(ll n, const lvec &mf) {
  palivec plist;
  while (n != 1) {
    int cnt = 0;
    ll m = mf[n];
    while (mf[n] == m) {
      cnt++;
      n /= m;
    }
    plist.pb(pali(m, cnt));
  }
  return plist;
}

void COMinit(int m, lvec &fac, lvec &finv) {
  lvec inv(m);
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < m; 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;
  }
}

ll pow_mod(ll a, ll n) {
  ll x = 1;
  while (n > 0) {
    if (n & 1) {
      x = x * a % MOD;
    }
    a = a * a % MOD;
    n >>= 1;
  }
  return x;
}

ll COM(int n, int k, const lvec &fac, const lvec &finv) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

ll modinv(ll a, ll m) {
  ll b = m, u = 1, v = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}

ll P(ll n, ll m) {
  ll s = 1;
  ll cnt = n;
  REP(i, n - m) {
    s *= cnt % MOD;
    s %= MOD;
    --cnt;
  }
  return s;
}

void fac(int a, int b, bvec &fmap) {
  for (int i = 2; i < b; i++) {
    if (fmap[i])
      continue;
    else if (a % i == 0) {
      fmap[i] = true;
      int n = a / i, x = i;
      while (n >= i) {
        n /= i;
        x += i;
        fmap[x] = true;
      }
    }
  }
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  ivec a(m + 1);
  for (int i = 0; i < m; i++) {
    cin >> a[i];
  }
  a[m] = n + 1;
  lvec dp(n + 1);
  dp[0] = 1;
  dp[1] = 1;
  for (int i = 2; i < n + 1; i++) {
    dp[i] = dp[i - 1] + dp[i - 2];
    dp[i] %= MOD;
  }
  ll ans = 1;
  int c = 0;
  for (int i = 0; i < m + 1; i++) {
    int ns = a[i] - c - 1;
    if (ns < 0) {
      cout << 0 << endl;
      return 0;
    }
    ans *= dp[ns];
    ans %= MOD;
    c = a[i] + 1;
  }

  /*
  lvec fac(n+1), finv(n+1);
  COMinit(n+1, fac, finv);
  int c=0;
  ll ans=1;
  for (int i=0; i<m+1; i++){
      int ns = a[i]-c-1;
      if(ns<0) {
          cout << 0 << endl;
          return 0;
      }
      int n2=0;
      int nss = ns;
      ll tmp=0;
      while(((nss >= n2)&&!(ns%2)) || ((nss > n2)&&(ns%2))){
          //cout << nss << ' ' << n2 << endl;
          tmp+=COM(nss, n2, fac, finv);
          ++n2;
          --nss;
      }
      ans*=tmp;
      ans%=MOD;
      c = a[i]+1;
  }
  */
  cout << ans << endl;
}