Problem p02661 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
#define rep2(i, s, n) for (int i = (s); i < (n); ++i)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define pb push_back
#define eb emplace_back
#define vi vector<int>
#define vvi vector<vector<int>>
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vd vector<double>
#define vs vector<string>
#define vc vector<char>
#define vb vector<bool>
#define vp vector<P>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using LP = pair<ll, ll>;
template <class S, class T> istream &operator>>(istream &is, pair<S, T> &p) {
  return is >> p.first >> p.second;
}
template <class S, class T>
ostream &operator<<(ostream &os, const pair<S, T> &p) {
  return os << '{' << p.first << "," << p.second << '}';
}
template <class T> istream &operator>>(istream &is, vector<T> &v) {
  for (T &t : v) {
    is >> t;
  }
  return is;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << '[';
  rep(i, v.size()) os << v[i] << (i == v.size() - 1 ? ']' : ',');
  return os;
}
void Yes(bool b) { cout << (b ? "Yes" : "No") << endl; }
void YES(bool b) { cout << (b ? "YES" : "NO") << endl; }
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
const int inf = 1001001001;
const ll linf = 1001001001001001001;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int n;
  cin >> n;
  vi a(n), b(n);
  rep(i, n) cin >> a[i] >> b[i];
  sort(all(a));
  sort(all(b));
  if (n & 1) {
    cout << b[n / 2] - a[n / 2] + 1 << endl;
  } else {
    cout << (b[n / 2] + b[n / 2 - 1]) - (a[n / 2] + a[n / 2 - 1]) + 1 << endl;
  }
}

Error: -6
fb85e31b-80e5-434e-afb3-7043fbb1d1f3.out: /home/alex/Documents/bug-detection/input/Project_CodeNet/data/p02661/C++/s285965899.cpp:40: int main(): Assertion `false' failed.


Fixed submission:

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
#define rep2(i, s, n) for (int i = (s); i < (n); ++i)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define pb push_back
#define eb emplace_back
#define vi vector<int>
#define vvi vector<vector<int>>
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vd vector<double>
#define vs vector<string>
#define vc vector<char>
#define vb vector<bool>
#define vp vector<P>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using LP = pair<ll, ll>;
template <class S, class T> istream &operator>>(istream &is, pair<S, T> &p) {
  return is >> p.first >> p.second;
}
template <class S, class T>
ostream &operator<<(ostream &os, const pair<S, T> &p) {
  return os << '{' << p.first << "," << p.second << '}';
}
template <class T> istream &operator>>(istream &is, vector<T> &v) {
  for (T &t : v) {
    is >> t;
  }
  return is;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << '[';
  rep(i, v.size()) os << v[i] << (i == v.size() - 1 ? ']' : ',');
  return os;
}
void Yes(bool b) { cout << (b ? "Yes" : "No") << endl; }
void YES(bool b) { cout << (b ? "YES" : "NO") << endl; }
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
const int inf = 1001001001;
const ll linf = 1001001001001001001;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int n;
  cin >> n;
  vi a(n), b(n);
  rep(i, n) cin >> a[i] >> b[i];
  if (n % 2 == 0)
    assert(false);
  vi v;
  rep(i, n) {
    v.pb(a[i]);
    v.pb(b[i]);
  }
  sort(all(v));
  v.erase(unique(all(v)), v.end());
  int ans = 0;
  int sz = v.size();
  vi le(sz, 0), ri(sz, 0);
  rep(i, n) {
    int pos = lower_bound(all(v), b[i]) - v.begin();
    le[pos]++;
    pos = lower_bound(all(v), a[i]) - v.begin();
    ri[pos]++;
  }
  rep(i, sz - 1) le[i + 1] += le[i];
  rrep(i, sz - 1) ri[i] += ri[i + 1];
  rep(i, sz - 1) {
    int l = v[i], r = v[i + 1];
    if (n % 2 == 1) {
      if (le[i] <= (n + 1) / 2 && ri[i] <= (n + 1) / 2)
        ans += 1;
      if (le[i] <= n / 2 && ri[i + 1] <= n / 2)
        ans += r - l - 1;
    } else {
      if (le[i] <= n / 2 && ri[i] <= n / 2)
        ans += 1;
      if (le[i] <= n / 2 - 1 && ri[i + 1] <= n / 2 - 1)
        ans += (r - l) * 2 - 1;
      else if (le[i] <= n / 2 - 1 && ri[i + 1] <= n / 2)
        ans += (r - l);
      else if (le[i] <= n / 2 && ri[i + 1] <= n / 2 - 1)
        ans += (r - l);
    }
  }
  int cnt = 0;
  rep(i, n) if (b[i] == v[sz - 1]) cnt++;
  if (cnt >= n / 2 + 1)
    ans++;
  cout << ans << endl;
}