Problem p03013 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <ctime>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <vector>

using namespace std;
using ll = long long;

#define REP(i, a) for (int i = 0; i < (a); ++i)
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORR(i, a, b) for (int i = (a)-1; i >= (b); --i)
#define ALL(obj) (obj).begin(), (obj).end()
#define SIZE(obj) (int)(obj).sizeT()
#define YESNO(cond, yes, no)                                                   \
  { cout << ((cond) ? (yes) : (no)) << endl; }
#define SORT(list) sort(ALL((list)));
#define RSORT(list) sort((list).rbegin(), (list).rend())
#define ASSERT(cond, mes) assert(cond &&mes)

constexpr int MOD = 1'000'000'007;
constexpr int INF = 1'050'000'000;

template <typename T> T round_up(const T &a, const T &b) {
  return (a + (b - 1)) / b;
}

template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}

template <typename T1, typename T2>
ostream &operator<<(ostream &os, pair<T1, T2> &p) {
  os << p.first << p.second;
  return os;
}

template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  REP(i, (int)v.size())
  is >> v[i];
  return is;
}

template <typename T> T clamp(T &n, T a, T b) {
  if (n < a)
    n = a;
  if (n > b)
    n = b;
  return n;
}

template <typename T> static T GCD(T u, T v) {
  T r;
  while (v != 0) {
    r = u % v;
    u = v;
    v = r;
  }
  return u;
}

template <typename T> static T LCM(T u, T v) { return u / GCD(u, v) * v; }

std::vector<int> enum_div(int n) {
  std::vector<int> ret;
  for (int i = 1; i * i <= n; ++i) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i != 1 && i * i != n) {
        ret.push_back(n / i);
      }
    }
  }
  return ret;
}

template <typename T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

struct ToUpper {
  char operator()(char c) { return toupper(c); }
};

struct ToLower {
  char operator()(char c) { return tolower(c); }
};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(20);

  int N, M;
  cin >> N >> M;

  vector<int> A(M);
  REP(i, M) { cin >> A[i]; }

  vector<ll> dp(N + 1);
  int step = 0;
  REP(i, N + 1) {
    if (A[step] == i) {
      step++;
      if (step >= M)
        step = 0;
      continue;
    }
    if (i == 0) {
      dp[i] = 1;
    } else if (i == 1) {
      dp[i] = 1;
    } else {
      dp[i] = dp[i - 1] + dp[i - 2];
    }
    dp[i] %= MOD;
  }

  cout << dp[N] << endl;
  return 0;
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <ctime>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <vector>

using namespace std;
using ll = long long;

#define REP(i, a) for (int i = 0; i < (a); ++i)
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORR(i, a, b) for (int i = (a)-1; i >= (b); --i)
#define ALL(obj) (obj).begin(), (obj).end()
#define SIZE(obj) (int)(obj).sizeT()
#define YESNO(cond, yes, no)                                                   \
  { cout << ((cond) ? (yes) : (no)) << endl; }
#define SORT(list) sort(ALL((list)));
#define RSORT(list) sort((list).rbegin(), (list).rend())
#define ASSERT(cond, mes) assert(cond &&mes)

constexpr int MOD = 1'000'000'007;
constexpr int INF = 1'050'000'000;

template <typename T> T round_up(const T &a, const T &b) {
  return (a + (b - 1)) / b;
}

template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}

template <typename T1, typename T2>
ostream &operator<<(ostream &os, pair<T1, T2> &p) {
  os << p.first << p.second;
  return os;
}

template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  REP(i, (int)v.size())
  is >> v[i];
  return is;
}

template <typename T> T clamp(T &n, T a, T b) {
  if (n < a)
    n = a;
  if (n > b)
    n = b;
  return n;
}

template <typename T> static T GCD(T u, T v) {
  T r;
  while (v != 0) {
    r = u % v;
    u = v;
    v = r;
  }
  return u;
}

template <typename T> static T LCM(T u, T v) { return u / GCD(u, v) * v; }

std::vector<int> enum_div(int n) {
  std::vector<int> ret;
  for (int i = 1; i * i <= n; ++i) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i != 1 && i * i != n) {
        ret.push_back(n / i);
      }
    }
  }
  return ret;
}

template <typename T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

struct ToUpper {
  char operator()(char c) { return toupper(c); }
};

struct ToLower {
  char operator()(char c) { return tolower(c); }
};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(20);

  int N, M;
  cin >> N >> M;

  vector<int> A(M);
  REP(i, M) { cin >> A[i]; }

  vector<ll> dp(N + 1);
  int step = 0;
  REP(i, N + 1) {
    if (A.size() > 0 && A[step] == i) {
      step++;
      if (step >= M)
        step = 0;
      continue;
    }
    if (i == 0) {
      dp[i] = 1;
    } else if (i == 1) {
      dp[i] = 1;
    } else {
      dp[i] = dp[i - 1] + dp[i - 2];
    }
    dp[i] %= MOD;
  }

  cout << dp[N] << endl;
  return 0;
}