Problem p02537 (C++)

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

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for (int i = ((int)(n)-1); i >= 0; i--)
#define irep(itr, st) for (auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for (auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define whole(x) (x).begin(), (x).end()
#define sz(x) ((int)(x).size())
#define bit(n) (1LL << (n))
#define F first
#define S second
// functions
template <typename T> void unique(T &c) {
  c.erase(std::unique(c.begin(), c.end()), c.end());
}
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;
}
template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (auto &v : vec)
    is >> v;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  for (int i = 0; i < vec.size(); i++) {
    os << vec[i];
    if (i + 1 != vec.size())
      os << " ";
  }
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const set<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end())
      os << " ";
  }
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const unordered_set<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end())
      os << " ";
  }
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end())
      os << " ";
  }
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const unordered_multiset<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end())
      os << " ";
  }
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const map<T1, T2> &mp) {
  for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
    os << "(" << itr->first << ", " << itr->second << ")";
    auto titr = itr;
    if (++titr != mp.end())
      os << " ";
  }
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp) {
  for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
    os << "(" << itr->first << ", " << itr->second << ")";
    auto titr = itr;
    if (++titr != mp.end())
      os << " ";
  }
  return os;
}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 60;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io {
  fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(20);
  }
} fast_io_;

template <class Monoid> class SegmentTree {
public:
  int n;
  using T = typename Monoid::value_type;
  vector<T> val;
  T identity;

  SegmentTree() {}
  SegmentTree(int n_, vector<T> v = vector<T>()) {
    n = 1;
    while (n < n_)
      n *= 2;
    identity = Monoid::identity;
    val.assign(2 * n - 1, identity);

    for (size_t i = 0; i < v.size(); i++) {
      val[i + n - 1] = v[i];
    }
    for (int i = n - 2; i >= 0; i--) {
      val[i] = Monoid::operation(val[2 * i + 1], val[2 * i + 2]);
    }
  }
  void update(int k, const T &t) {
    k = k + n - 1;
    val[k] = t;
    while (k > 0) {
      k = (k - 1) / 2;
      val[k] = Monoid::operation(val[2 * k + 1], val[2 * k + 2]);
    }
  }
  T query(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l)
      return identity;
    if (a <= l && r <= b)
      return val[k];
    T lv = query(a, b, 2 * k + 1, l, (l + r) / 2);
    T rv = query(a, b, 2 * k + 2, (l + r) / 2, r);
    return Monoid::operation(lv, rv);
  }
  T query(int a, int b) { return query(a, b, 0, 0, n); }
  T get(int i) { return val[i + n - 1]; }
};

template <typename T> class RMQ {
public:
  const static T identity;
  using value_type = T;

  RMQ() {}
  static T operation(T &l, T &r) { return max(l, r); }
};

template <typename T> const T RMQ<T>::identity = numeric_limits<T>::min();

const int B = 300010;

int main(int argc, char const *argv[]) {
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  cin >> a;
  SegmentTree<RMQ<int>> seg(n);
  int res = 0;
  rep(i, n) {
    int l = max(0, a[i] - k);
    int r = min(a[i] + k, B - 1);
    int p = seg.query(l, r + 1);
    if (p == seg.identity)
      p = 0;
    p++;
    seg.update(a[i], p);
    chmax(res, p);
  }
  cout << res << endl;
  return 0;
}


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

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for (int i = ((int)(n)-1); i >= 0; i--)
#define irep(itr, st) for (auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for (auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define whole(x) (x).begin(), (x).end()
#define sz(x) ((int)(x).size())
#define bit(n) (1LL << (n))
#define F first
#define S second
// functions
template <typename T> void unique(T &c) {
  c.erase(std::unique(c.begin(), c.end()), c.end());
}
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;
}
template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (auto &v : vec)
    is >> v;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  for (int i = 0; i < vec.size(); i++) {
    os << vec[i];
    if (i + 1 != vec.size())
      os << " ";
  }
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const set<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end())
      os << " ";
  }
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const unordered_set<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end())
      os << " ";
  }
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end())
      os << " ";
  }
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const unordered_multiset<T> &st) {
  for (auto itr = st.begin(); itr != st.end(); ++itr) {
    os << *itr;
    auto titr = itr;
    if (++titr != st.end())
      os << " ";
  }
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const map<T1, T2> &mp) {
  for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
    os << "(" << itr->first << ", " << itr->second << ")";
    auto titr = itr;
    if (++titr != mp.end())
      os << " ";
  }
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp) {
  for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
    os << "(" << itr->first << ", " << itr->second << ")";
    auto titr = itr;
    if (++titr != mp.end())
      os << " ";
  }
  return os;
}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 60;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io {
  fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(20);
  }
} fast_io_;

template <class Monoid> class SegmentTree {
public:
  int n;
  using T = typename Monoid::value_type;
  vector<T> val;
  T identity;

  SegmentTree() {}
  SegmentTree(int n_, vector<T> v = vector<T>()) {
    n = 1;
    while (n < n_)
      n *= 2;
    identity = Monoid::identity;
    val.assign(2 * n - 1, identity);

    for (size_t i = 0; i < v.size(); i++) {
      val[i + n - 1] = v[i];
    }
    for (int i = n - 2; i >= 0; i--) {
      val[i] = Monoid::operation(val[2 * i + 1], val[2 * i + 2]);
    }
  }
  void update(int k, const T &t) {
    k = k + n - 1;
    val[k] = t;
    while (k > 0) {
      k = (k - 1) / 2;
      val[k] = Monoid::operation(val[2 * k + 1], val[2 * k + 2]);
    }
  }
  T query(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l)
      return identity;
    if (a <= l && r <= b)
      return val[k];
    T lv = query(a, b, 2 * k + 1, l, (l + r) / 2);
    T rv = query(a, b, 2 * k + 2, (l + r) / 2, r);
    return Monoid::operation(lv, rv);
  }
  T query(int a, int b) { return query(a, b, 0, 0, n); }
  T get(int i) { return val[i + n - 1]; }
};

template <typename T> class RMQ {
public:
  const static T identity;
  using value_type = T;

  RMQ() {}
  static T operation(T &l, T &r) { return max(l, r); }
};

template <typename T> const T RMQ<T>::identity = numeric_limits<T>::min();

const int B = 300010;

int main(int argc, char const *argv[]) {
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  cin >> a;
  SegmentTree<RMQ<int>> seg(B);
  int res = 0;
  rep(i, n) {
    int l = max(0, a[i] - k);
    int r = min(a[i] + k, B - 1);
    int p = seg.query(l, r + 1);
    if (p == seg.identity)
      p = 0;
    p++;
    seg.update(a[i], p);
    chmax(res, p);
  }
  cout << res << endl;
  return 0;
}