Problem p03013 (C++)

Buggy submission (status: Runtime Error):
#include <stdio.h>

#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }

template <typename T, typename V> void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T> void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x)
    cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\n"; }
template <typename T, typename... V> void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v))
    cerr << ", ";
  _print(v...);
}
#ifdef LOCAL
#define debug(x...)                                                            \
  cerr << "[" << #x << "] = [";                                                \
  _print(x)
#else
#define debug(x...)
#endif

#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());
#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)

typedef long long ll;

ll N, M;
ll steps[1000001];
ll MOD = 1000000007;

priority_queue<ll, vector<ll>, greater<ll>> a;

void dp(ll current) {
  ll next;
  if (!a.empty()) {
    next = a.top();
  } else {
    next = -1;
  }
  if (current == next) {
    steps[current] = 0;
    a.pop();
  } else {
    steps[current] = (steps[current - 1] + steps[current - 2]) % MOD;
  }
  if (current == N)
    return;
  dp(current + 1);
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> N >> M;
  REP(i, M) {
    ll tmp;
    cin >> tmp;
    a.push(tmp);
  }
  steps[0] = 1;
  if (M == 0) {
    steps[1] = 1;
  } else {
    if (a.top() == 1) {
      a.pop();
      steps[1] = 0;
    } else {
      steps[1] = 1;
    }
  }
  dp(2);
  cout << steps[N] % MOD << endl;

  return 0;
}


Fixed submission:
#include <stdio.h>

#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }

template <typename T, typename V> void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T> void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x)
    cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\n"; }
template <typename T, typename... V> void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v))
    cerr << ", ";
  _print(v...);
}
#ifdef LOCAL
#define debug(x...)                                                            \
  cerr << "[" << #x << "] = [";                                                \
  _print(x)
#else
#define debug(x...)
#endif

#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());
#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)

typedef long long ll;

ll N, M;
ll steps[1000001];
ll MOD = 1000000007;

priority_queue<ll, vector<ll>, greater<ll>> a;

void dp(ll current) {
  ll next;
  if (!a.empty()) {
    next = a.top();
  } else {
    next = -1;
  }
  if (current == next) {
    steps[current] = 0;
    a.pop();
  } else {
    steps[current] = (steps[current - 1] + steps[current - 2]) % MOD;
  }
  if (current == N)
    return;
  dp(current + 1);
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> N >> M;
  REP(i, M) {
    ll tmp;
    cin >> tmp;
    a.push(tmp);
  }
  steps[0] = 1;
  if (M == 0) {
    steps[1] = 1;
  } else {
    if (a.top() == 1) {
      a.pop();
      steps[1] = 0;
    } else {
      steps[1] = 1;
    }
  }
  if (N == 1) {
    cout << steps[1] << endl;
  } else {
    dp(2);
    cout << steps[N] % MOD << endl;
  }

  return 0;
}