Problem p02679 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define FOR(i, n, m) for (int i = (int)(n); i <= (int)(m); i++)
#define RFOR(i, n, m) for (int i = (int)(n); i >= (int)(m); i--)
#define ITR(x, c) for (__typeof(c.begin()) x = c.begin(); x != c.end(); x++)
#define RITR(x, c) for (__typeof(c.rbegin()) x = c.rbegin(); x != c.rend(); x++)
#define setp(n) fixed << setprecision(n)

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

#define ll long long
#define vll vector<ll>
#define vi vector<int>
#define pll pair<ll, ll>
#define pi pair<int, int>

#define all(a) (a.begin()), (a.end())
#define rall(a) (a.rbegin()), (a.rend())
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define ins insert

using namespace std;

//-------------------------------------------------
//--ModInt
//-------------------------------------------------
const ::std::uint_fast64_t MOD = 1e9 + 7;

class mint {
private:
  using value_type = ::std::uint_fast64_t;
  value_type n;

public:
  mint() : n(0) {}
  mint(::std::int_fast64_t _n) : n(_n < 0 ? MOD - (-_n) % MOD : _n % MOD) {}
  mint(const mint &m) : n(m.n) {}

  friend ::std::ostream &operator<<(::std::ostream &os, const mint &a) {
    return os << a.n;
  }
  friend ::std::istream &operator>>(::std::istream &is, mint &a) {
    value_type temp;
    is >> temp;
    a = mint(temp);
    return is;
  }

  mint &operator+=(const mint &m) {
    n += m.n;
    n = (n < MOD) ? n : n - MOD;
    return *this;
  }
  mint &operator-=(const mint &m) {
    n += MOD - m.n;
    n = (n < MOD) ? n : n - MOD;
    return *this;
  }
  mint &operator*=(const mint &m) {
    n = n * m.n % MOD;
    return *this;
  }
  mint &operator/=(const mint &m) { return *this *= m.inv(); }
  mint &operator++() { return *this += 1; }
  mint &operator--() { return *this -= 1; }

  mint operator+(const mint &m) const { return mint(*this) += m; }
  mint operator-(const mint &m) const { return mint(*this) -= m; }
  mint operator*(const mint &m) const { return mint(*this) *= m; }
  mint operator/(const mint &m) const { return mint(*this) /= m; }
  mint operator++(int) {
    mint t(*this);
    *this += 1;
    return t;
  }
  mint operator--(int) {
    mint t(*this);
    *this -= 1;
    return t;
  }

  bool operator==(const mint &m) const { return n == m.n; }
  bool operator!=(const mint &m) const { return n != m.n; }
  mint operator-() const { return mint(MOD - n); }

  mint pow(value_type b) const {
    mint ret(1), m(*this);
    while (b) {
      if (b & 1)
        ret *= m;
      m *= m;
      b >>= 1;
    }
    return ret;
  }

  mint inv() const { return pow(MOD - 2); }
};

//-------------------------------------------------

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int N;
  cin >> N;
  map<pll, int> M;
  ll cnt = 0;
  rep(i, N) {
    ll a, b;
    cin >> a >> b;
    if (a == 0 && b == 0) {
      cnt++;
      continue;
    }
    ll g = __gcd(a, b);
    M[mp(a / g, b / g)]++;
  }
  vector<pll> events;
  for (auto e : M) {
    auto v = e.fi;
    if (v.se <= 0) {
      int t = M[mp(-v.se, v.fi)];
      events.pb({e.se, t});
      M.erase(mp(-v.se, v.fi));
    } else {
      int t = M[mp(v.se, -v.fi)];
      events.pb({e.se, t});
      M.erase(mp(v.se, -v.fi));
    }
  }
  mint ans = 1;
  for (auto e : events) {
    ans *= mint(2).pow(e.fi) + mint(2).pow(e.se) - 1;
  }
  cout << ans + cnt - 1 << "\\n";
  return 0;
}


Error: WA

Fixed submission:

#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define FOR(i, n, m) for (int i = (int)(n); i <= (int)(m); i++)
#define RFOR(i, n, m) for (int i = (int)(n); i >= (int)(m); i--)
#define ITR(x, c) for (__typeof(c.begin()) x = c.begin(); x != c.end(); x++)
#define RITR(x, c) for (__typeof(c.rbegin()) x = c.rbegin(); x != c.rend(); x++)
#define setp(n) fixed << setprecision(n)

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

#define ll long long
#define vll vector<ll>
#define vi vector<int>
#define pll pair<ll, ll>
#define pi pair<int, int>

#define all(a) (a.begin()), (a.end())
#define rall(a) (a.rbegin()), (a.rend())
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define ins insert

using namespace std;

//-------------------------------------------------

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  vector<vi> adj(n);
  rep(i, m) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    adj[a].pb(b);
    adj[b].pb(a);
  }
  vi dep(n, -1);
  queue<int> que;
  dep[0] = 0;
  que.push(0);
  while (que.size()) {
    int v = que.front();
    que.pop();
    for (auto u : adj[v]) {
      if (dep[u] != -1)
        continue;
      dep[u] = dep[v] + 1;
      que.push(u);
    }
  }
  cout << "Yes\\n";
  vi ans(n);
  FOR(i, 1, n - 1) {
    for (auto u : adj[i]) {
      if (dep[u] == dep[i] - 1) {
        cout << u + 1 << "\\n";
        break;
      }
    }
  }
  return 0;
}