Problem p04017 (C++)

Buggy submission (status: Runtime Error):
// >>> TEMPLATES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using i32 = int32_t;
using i64 = int64_t;
#define int ll
#define double ld
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define repR(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep1R(i, n) for (int i = (int)(n); i >= 1; i--)
#define loop(i, a, B) for (int i = a; i B; i++)
#define loopR(i, a, B) for (int i = a; i B; i--)
#define all(x) (x).begin(), (x).end()
#define allR(x) (x).rbegin(), (x).rend()
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fst first
#define snd second
#define INF32 (numeric_limits<int32_t>::max() / 2 - 1)
#define INF64 (numeric_limits<int64_t>::max() / 2 - 1)
#define INF (numeric_limits<int>::max() / 2 - 1)
#ifdef LOCAL
#include "debug.hpp"
#define dump(...)                                                              \
  cerr << "[" << setw(3) << __LINE__ << ":" << __FUNCTION__ << "] ",           \
      dump_impl(#__VA_ARGS__, __VA_ARGS__)
#define say(x)                                                                 \
  cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] " << x << endl
#define debug if (1)
#else
#define dump(...) (void)(0)
#define say(x) (void)(0)
#define debug if (0)
#endif
template <class T> using pque_max = priority_queue<T>;
template <class T> using pque_min = priority_queue<T, vector<T>, greater<T>>;
template <class T, class = typename T::iterator,
          class = typename enable_if<!is_same<T, string>::value>::type>
ostream &operator<<(ostream &os, T const &v) {
  bool f = true;
  for (auto const &x : v)
    os << (f ? "" : " ") << x, f = false;
  return os;
}
template <class T, class = typename T::iterator,
          class = typename enable_if<!is_same<T, string>::value>::type>
istream &operator>>(istream &is, T &v) {
  for (auto &x : v)
    is >> x;
  return is;
}
template <class T, class S> istream &operator>>(istream &is, pair<T, S> &p) {
  return is >> p.first >> p.second;
}
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(15);
  }
} iosetup;
template <class F> struct FixPoint : private F {
  constexpr FixPoint(F &&f) : F(forward<F>(f)) {}
  template <class... T> constexpr auto operator()(T &&...x) const {
    return F::operator()(*this, forward<T>(x)...);
  }
};
struct MakeFixPoint {
  template <class F> constexpr auto operator|(F &&f) const {
    return FixPoint<F>(forward<F>(f));
  }
};
#define MFP MakeFixPoint() |
#define def(name, ...) auto name = MFP[&](auto &&name, __VA_ARGS__)
template <class T, size_t d> struct vec_impl {
  using type = vector<typename vec_impl<T, d - 1>::type>;
  template <class... U> static type make_v(size_t n, U &&...x) {
    return type(n, vec_impl<T, d - 1>::make_v(forward<U>(x)...));
  }
};
template <class T> struct vec_impl<T, 0> {
  using type = T;
  static type make_v(T const &x = {}) { return x; }
};
template <class T, size_t d = 1> using vec = typename vec_impl<T, d>::type;
template <class T, size_t d = 1, class... Args> auto make_v(Args &&...args) {
  return vec_impl<T, d>::make_v(forward<Args>(args)...);
}
template <class T> void quit(T const &x) {
  cout << x << endl;
  exit(0);
}
template <class T> constexpr bool chmin(T &x, T const &y) {
  if (x > y) {
    x = y;
    return true;
  }
  return false;
}
template <class T> constexpr bool chmax(T &x, T const &y) {
  if (x < y) {
    x = y;
    return true;
  }
  return false;
}
template <class It> constexpr auto sumof(It b, It e) {
  return accumulate(b, e, typename iterator_traits<It>::value_type{});
}
template <class T> int sz(T const &x) { return x.size(); }
template <class C, class T> int lbd(C const &v, T const &x) {
  return lower_bound(v.begin(), v.end(), x) - v.begin();
}
template <class C, class T> int ubd(C const &v, T const &x) {
  return upper_bound(v.begin(), v.end(), x) - v.begin();
}
// <<<

int32_t main() {
  int n;
  cin >> n;
  vector<int> x(n);
  cin >> x;
  int L;
  cin >> L;

  const int LG = 23;
  auto dp = make_v<int, 2>(LG, n);
  {
    int j = 0;
    rep(i, n) {
      while (j + 1 < n && x[j + 1] <= x[i] + L)
        j++;
      dp[0][i] = j;

      assert(x[j] <= x[i] + L);
      if (j < n - 1)
        assert(x[j + 1] > x[i] + L);
    }
    dump(dp[0]);
  }
  rep(i, LG - 1) rep(j, n) { dp[i + 1][j] = dp[i][dp[i][j]]; }
  auto go = [&](int k, int from) {
    int i = 0;
    for (; k; k >>= 1, ++i)
      if (k & 1)
        from = dp[i][from];
    return from;
  };

  int q;
  cin >> q;
  rep(_, q) {
    int a, b;
    cin >> a >> b;
    a--, b--;
    if (a > b)
      swap(a, b);

    // int cnt = 0;
    // repR (j,LG-1) {
    //     if (dp[j][a] <= b) {
    //         a = dp[j][a];
    //         cnt ^= (1LL<<j);
    //     }
    //     if (a == b) break;
    // }
    // assert(a == b);
    // cout << cnt << "\n";

    int l = 0, r = n;
    while (l + 1 < r) {
      int mid = (l + r) / 2;
      (go(mid, a) < b ? l : r) = mid;
    }
    assert(go(r, a) == b);
    cout << r << "\n";
  }
}


Fixed submission:
// >>> TEMPLATES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using i32 = int32_t;
using i64 = int64_t;
#define int ll
#define double ld
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define repR(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep1R(i, n) for (int i = (int)(n); i >= 1; i--)
#define loop(i, a, B) for (int i = a; i B; i++)
#define loopR(i, a, B) for (int i = a; i B; i--)
#define all(x) (x).begin(), (x).end()
#define allR(x) (x).rbegin(), (x).rend()
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fst first
#define snd second
#define INF32 (numeric_limits<int32_t>::max() / 2 - 1)
#define INF64 (numeric_limits<int64_t>::max() / 2 - 1)
#define INF (numeric_limits<int>::max() / 2 - 1)
#ifdef LOCAL
#include "debug.hpp"
#define dump(...)                                                              \
  cerr << "[" << setw(3) << __LINE__ << ":" << __FUNCTION__ << "] ",           \
      dump_impl(#__VA_ARGS__, __VA_ARGS__)
#define say(x)                                                                 \
  cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] " << x << endl
#define debug if (1)
#else
#define dump(...) (void)(0)
#define say(x) (void)(0)
#define debug if (0)
#endif
template <class T> using pque_max = priority_queue<T>;
template <class T> using pque_min = priority_queue<T, vector<T>, greater<T>>;
template <class T, class = typename T::iterator,
          class = typename enable_if<!is_same<T, string>::value>::type>
ostream &operator<<(ostream &os, T const &v) {
  bool f = true;
  for (auto const &x : v)
    os << (f ? "" : " ") << x, f = false;
  return os;
}
template <class T, class = typename T::iterator,
          class = typename enable_if<!is_same<T, string>::value>::type>
istream &operator>>(istream &is, T &v) {
  for (auto &x : v)
    is >> x;
  return is;
}
template <class T, class S> istream &operator>>(istream &is, pair<T, S> &p) {
  return is >> p.first >> p.second;
}
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(15);
  }
} iosetup;
template <class F> struct FixPoint : private F {
  constexpr FixPoint(F &&f) : F(forward<F>(f)) {}
  template <class... T> constexpr auto operator()(T &&...x) const {
    return F::operator()(*this, forward<T>(x)...);
  }
};
struct MakeFixPoint {
  template <class F> constexpr auto operator|(F &&f) const {
    return FixPoint<F>(forward<F>(f));
  }
};
#define MFP MakeFixPoint() |
#define def(name, ...) auto name = MFP[&](auto &&name, __VA_ARGS__)
template <class T, size_t d> struct vec_impl {
  using type = vector<typename vec_impl<T, d - 1>::type>;
  template <class... U> static type make_v(size_t n, U &&...x) {
    return type(n, vec_impl<T, d - 1>::make_v(forward<U>(x)...));
  }
};
template <class T> struct vec_impl<T, 0> {
  using type = T;
  static type make_v(T const &x = {}) { return x; }
};
template <class T, size_t d = 1> using vec = typename vec_impl<T, d>::type;
template <class T, size_t d = 1, class... Args> auto make_v(Args &&...args) {
  return vec_impl<T, d>::make_v(forward<Args>(args)...);
}
template <class T> void quit(T const &x) {
  cout << x << endl;
  exit(0);
}
template <class T> constexpr bool chmin(T &x, T const &y) {
  if (x > y) {
    x = y;
    return true;
  }
  return false;
}
template <class T> constexpr bool chmax(T &x, T const &y) {
  if (x < y) {
    x = y;
    return true;
  }
  return false;
}
template <class It> constexpr auto sumof(It b, It e) {
  return accumulate(b, e, typename iterator_traits<It>::value_type{});
}
template <class T> int sz(T const &x) { return x.size(); }
template <class C, class T> int lbd(C const &v, T const &x) {
  return lower_bound(v.begin(), v.end(), x) - v.begin();
}
template <class C, class T> int ubd(C const &v, T const &x) {
  return upper_bound(v.begin(), v.end(), x) - v.begin();
}
// <<<

int32_t main() {
  int n;
  cin >> n;
  vector<int> x(n);
  cin >> x;
  int L;
  cin >> L;

  const int LG = 23;
  auto dp = make_v<int, 2>(LG, n);
  {
    int j = 0;
    rep(i, n) {
      while (j + 1 < n && x[j + 1] <= x[i] + L)
        j++;
      dp[0][i] = j;

      assert(x[j] <= x[i] + L);
      if (j < n - 1)
        assert(x[j + 1] > x[i] + L);
    }
    dump(dp[0]);
  }
  rep(i, LG - 1) rep(j, n) { dp[i + 1][j] = dp[i][dp[i][j]]; }
  auto go = [&](int k, int from) {
    int i = 0;
    for (; k; k >>= 1, ++i)
      if (k & 1)
        from = dp[i][from];
    return from;
  };

  int q;
  cin >> q;
  rep(_, q) {
    int a, b;
    cin >> a >> b;
    a--, b--;
    if (a > b)
      swap(a, b);

    // int cnt = 0;
    // repR (j,LG-1) {
    //     if (dp[j][a] <= b) {
    //         a = dp[j][a];
    //         cnt ^= (1LL<<j);
    //     }
    //     if (a == b) break;
    // }
    // assert(a == b);
    // cout << cnt << "\n";

    int l = 0, r = n;
    while (l + 1 < r) {
      int mid = (l + r) / 2;
      (go(mid, a) < b ? l : r) = mid;
    }
    //        assert(go(r,a) == b);
    cout << r << "\n";
  }
}