Problem p02776 (C++)

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

#define int long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define reps(i, n) for (int i = 1; i <= (n); i++)
#define all(x) begin(x), end(x)
#define uniq(x) (x).erase(unique(all(x)), end(x))
#define bit(n) (1LL << (n))
#define cdiv(a, b) (((a)-1) / (b) + 1)
#define dump(x) cerr << #x " = " << (x) << endl
using vint = vector<int>;
using vvint = vector<vint>;
using pint = pair<int, int>;
using vpint = vector<pint>;
template <typename T>
using priority_queue_rev = priority_queue<T, vector<T>, greater<T>>;
constexpr long double PI = 3.1415926535897932384626433832795028L;
constexpr int DY[8] = {0, 1, 0, -1, 1, 1, -1, -1};
constexpr int DX[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int gcd(int a, int b) {
  while (b) {
    swap(a %= b, b);
  }
  return a;
}
int lcm(int a, int b) { return a / gcd(a, b) * b; }
template <typename T> void fin(T mes) {
  cout << mes << endl;
  exit(0);
}
template <typename T, typename U> bool chmax(T &a, const U &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U> bool chmin(T &a, const U &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &rhs) {
  os << "(" << rhs.first << ", " << rhs.second << ")";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
struct setup {
  static constexpr int PREC = 20;
  setup() {
    cout << fixed << setprecision(PREC);
    cerr << fixed << setprecision(PREC);
  };
} setup;

int N, M;
int A[110000], B[110000];
int L[220000], R[220000];
pint AB[110000];
vpint G[110000];
bool sw[110000], visited[110000];
bool dfs(int cur, bool drop) {
  if (visited[cur]) {
    return drop;
  }
  visited[cur] = true;
  drop ^= AB[cur].second;
  rep(i, G[cur].size()) {
    sw[G[cur][i].second] ^= drop;
    drop = dfs(G[cur][i].first, drop);
    sw[G[cur][i].second] ^= drop;
  }
  return drop;
}
signed main() {
  cin >> N >> M;
  rep(i, N) {
    cin >> A[i] >> B[i];
    AB[i] = {A[i], B[i]};
  }
  sort(AB, AB + N);
  AB[N] = {LLONG_MAX, 0};
  for (int i = N; i > 0; i--) {
    AB[i].second ^= AB[i - 1].second;
  }
  rep(i, M) {
    cin >> L[i] >> R[i];
    int l = lower_bound(AB, AB + N + 1, pint(L[i], 0)) - AB;
    int r = upper_bound(AB, AB + N + 1, pint(R[i], LLONG_MAX)) - AB;
    if (l < r) {
      G[l].push_back({r, i}), G[r].push_back({l, i});
    }
  }
  rep(i, N + 1) {
    if (dfs(i, false)) {
      fin(-1);
    }
  }
  vint ans;
  rep(i, M) {
    if (sw[i]) {
      ans.push_back(i + 1);
    }
  }
  cout << ans.size() << endl;
  rep(i, ans.size()) { cout << ans[i] << " "; }
  cout << endl;
}

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

#define int long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define reps(i, n) for (int i = 1; i <= (n); i++)
#define all(x) begin(x), end(x)
#define uniq(x) (x).erase(unique(all(x)), end(x))
#define bit(n) (1LL << (n))
#define cdiv(a, b) (((a)-1) / (b) + 1)
#define dump(x) cerr << #x " = " << (x) << endl
using vint = vector<int>;
using vvint = vector<vint>;
using pint = pair<int, int>;
using vpint = vector<pint>;
template <typename T>
using priority_queue_rev = priority_queue<T, vector<T>, greater<T>>;
constexpr long double PI = 3.1415926535897932384626433832795028L;
constexpr int DY[8] = {0, 1, 0, -1, 1, 1, -1, -1};
constexpr int DX[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int gcd(int a, int b) {
  while (b) {
    swap(a %= b, b);
  }
  return a;
}
int lcm(int a, int b) { return a / gcd(a, b) * b; }
template <typename T> void fin(T mes) {
  cout << mes << endl;
  exit(0);
}
template <typename T, typename U> bool chmax(T &a, const U &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U> bool chmin(T &a, const U &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &rhs) {
  os << "(" << rhs.first << ", " << rhs.second << ")";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
struct setup {
  static constexpr int PREC = 20;
  setup() {
    cout << fixed << setprecision(PREC);
    cerr << fixed << setprecision(PREC);
  };
} setup;

int N, M;
int A[110000], B[110000];
int L[220000], R[220000];
pint AB[110000];
vpint G[110000];
bool sw[220000], visited[110000];
bool dfs(int cur, bool drop) {
  if (visited[cur]) {
    return drop;
  }
  visited[cur] = true;
  drop ^= AB[cur].second;
  rep(i, G[cur].size()) {
    sw[G[cur][i].second] ^= drop;
    drop = dfs(G[cur][i].first, drop);
    sw[G[cur][i].second] ^= drop;
  }
  return drop;
}
signed main() {
  cin >> N >> M;
  rep(i, N) {
    cin >> A[i] >> B[i];
    AB[i] = {A[i], B[i]};
  }
  sort(AB, AB + N);
  AB[N] = {LLONG_MAX, 0};
  for (int i = N; i > 0; i--) {
    AB[i].second ^= AB[i - 1].second;
  }
  rep(i, M) {
    cin >> L[i] >> R[i];
    int l = lower_bound(AB, AB + N + 1, pint(L[i], 0)) - AB;
    int r = upper_bound(AB, AB + N + 1, pint(R[i], LLONG_MAX)) - AB;
    if (l < r) {
      G[l].push_back({r, i}), G[r].push_back({l, i});
    }
  }
  rep(i, N + 1) {
    if (dfs(i, false)) {
      fin(-1);
    }
  }
  vint ans;
  rep(i, M) {
    if (sw[i]) {
      ans.push_back(i + 1);
    }
  }
  cout << ans.size() << endl;
  rep(i, ans.size()) { cout << ans[i] << " "; }
  cout << endl;
}