tpl_rbRk.H

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
*/
 
 
# ifndef TPL_RBRK_H
# define TPL_RBRK_H
 
# include <ahFunction.H>
# include <tpl_arrayStack.H>
# include <tpl_binNodeUtils.H>
# include <tpl_binNodeXt.H>
# include <tpl_binTreeOps.H>
# include <rbNodeRk.H>
# include <ah-errors.H>
 
namespace Aleph {
 
template <template <typename> class NodeType, typename Key, class Compare>
class Gen_Rb_Tree_Rk
{
public:
 
  typedef NodeType<Key> Node;
 
private:
 
  Node head_node;
  Node * head;
  Node *& root;
  FixedStack<Node *> rb_stack;
  Compare cmp;
  static constexpr signed char CmpLess = -1;
  static constexpr signed char CmpEqual = 0;
  static constexpr signed char CmpGreater = 1;
 
  Node * search_and_stack_rb(const Key & key,
                             signed char & cmp_result) noexcept
  {
    Node *p = root;
    Node *candidate = nullptr;  // Tracks potential duplicate when going right
    size_t candidate_pos = 0;   // Stack size when candidate was set
 
    rb_stack.push(head);
    do
      {
        rb_stack.push(p);
        if (cmp(key, KEY(p)))  // key < KEY(p)
          {
            cmp_result = CmpLess;
            p = LLINK(p);
          }
        else  // key >= KEY(p), could be equal
          {
            candidate = p;
            candidate_pos = rb_stack.size();
            cmp_result = CmpGreater;
            p = RLINK(p);
          }
      }
    while (p != Node::NullPtr);
 
    // Optimistic duplicate check: when going right, key >= KEY(candidate)
    // If also KEY(candidate) >= key (i.e., not less), then key == KEY(candidate)
    if (candidate != nullptr and not cmp(KEY(candidate), key)) [[unlikely]]
      {
        cmp_result = CmpEqual;
        // Truncate stack: remove nodes pushed after candidate
        rb_stack.popn(rb_stack.size() - candidate_pos);
        return candidate;
      }
 
    return rb_stack.top();
  }
 
  Node * search_dup_and_stack_rb(const Key & key,
                                 signed char & cmp_result)
  {
    Node * p = root;
    rb_stack.push(head);
    cmp_result = CmpEqual;
    do
      {
        rb_stack.push(p);
        const Key & pk = KEY(p);
        if (cmp(key, pk))
          {
            cmp_result = CmpLess;
            p = LLINK(p);
          }
        else
          {
            cmp_result = CmpGreater;
            p = RLINK(p);
          }
      }
    while (p != Node::NullPtr);
 
    return rb_stack.top();
  }
 
  // Rotate to right with counter update
  Node * rotate_to_right_rk(Node * p, Node * pp) noexcept
  {
    assert(p != Node::NullPtr);
    assert(pp != Node::NullPtr);
    assert(LLINK(pp) == p or RLINK(pp) == p);
 
    Node * q = LLINK(p);
    LLINK(p) = RLINK(q);
    RLINK(q) = p;
 
    // Update counters
    COUNT(p) = COUNT(LLINK(p)) + COUNT(RLINK(p)) + 1;
    COUNT(q) = COUNT(LLINK(q)) + COUNT(RLINK(q)) + 1;
 
    if (LLINK(pp) == p)
      LLINK(pp) = q;
    else
      RLINK(pp) = q;
 
    return q;
  }
 
  // Rotate to left with counter update
  Node * rotate_to_left_rk(Node * p, Node * pp) noexcept
  {
    assert(p != Node::NullPtr);
    assert(pp != Node::NullPtr);
    assert(LLINK(pp) == p or RLINK(pp) == p);
 
    Node * q = RLINK(p);
    RLINK(p) = LLINK(q);
    LLINK(q) = p;
 
    // Update counters
    COUNT(p) = COUNT(LLINK(p)) + COUNT(RLINK(p)) + 1;
    COUNT(q) = COUNT(LLINK(q)) + COUNT(RLINK(q)) + 1;
 
    if (LLINK(pp) == p)
      LLINK(pp) = q;
    else
      RLINK(pp) = q;
 
    return q;
  }
 
  void fix_red_condition(Node * p)
  {
    assert(COLOR(p) == RED);
 
    while (p != root)
      {
        Node * pp = rb_stack.pop();
        if (COLOR(pp) == BLACK)
          break;
 
        if (root == pp)
          {
            COLOR(root) = BLACK;
            break;
          }
 
        Node * ppp = rb_stack.pop();
        Node * spp = LLINK(ppp) == pp ? RLINK(ppp) : LLINK(ppp);
 
        if (COLOR(spp) == RED)
          {
            COLOR(ppp) = RED;
            COLOR(pp) = BLACK;
            COLOR(spp) = BLACK;
            p = ppp;
            continue;
          }
 
        Node * pppp = rb_stack.pop();
        if (LLINK(pp) == p and LLINK(ppp) == pp)
          {
            rotate_to_right_rk(ppp, pppp);
            COLOR(pp) = BLACK;
          }
        else if (RLINK(pp) == p and RLINK(ppp) == pp)
          {
            rotate_to_left_rk(ppp, pppp);
            COLOR(pp) = BLACK;
          }
        else
          {
            if (RLINK(pp) == p)
              {
                rotate_to_left_rk(pp, ppp);
                rotate_to_right_rk(ppp, pppp);
              }
            else
              {
                rotate_to_right_rk(pp, ppp);
                rotate_to_left_rk(ppp, pppp);
              }
            COLOR(p) = BLACK;
          }
 
        COLOR(ppp) = RED;
        break;
      }
 
    rb_stack.empty();
  }
 
  void find_succ_and_swap(Node * p, Node *& pp)
  {
    Node *& ref_rb_stack = rb_stack.top();
 
    Node * fSucc = p;
    Node * succ = RLINK(p);
    rb_stack.push(succ);
 
    while (LLINK(succ) != Node::NullPtr)
      {
        fSucc = succ;
        succ = LLINK(succ);
        rb_stack.push(succ);
      }
 
    ref_rb_stack = succ;
    rb_stack.top() = p;
 
    if (LLINK(pp) == p)
      LLINK(pp) = succ;
    else
      RLINK(pp) = succ;
 
    LLINK(succ) = LLINK(p);
    LLINK(p) = Node::NullPtr;
 
    if (RLINK(p) == succ)
      {
        RLINK(p) = RLINK(succ);
        RLINK(succ) = p;
        pp = succ;
      }
    else
      {
        Node * succr = RLINK(succ);
        RLINK(succ) = RLINK(p);
        LLINK(fSucc) = p;
        RLINK(p) = succr;
        pp = fSucc;
      }
 
    std::swap(COLOR(succ), COLOR(p));
    COUNT(succ) = COUNT(p);  // Copy counter to successor position
  }
 
  void fix_black_condition(Node * p)
  {
    if (COLOR(p) == RED)
      {
        COLOR(p) = BLACK;
        return;
      }
 
    Node * pp = rb_stack.popn(2);
    while (p != root)
      {
        assert(LLINK(pp) == p or RLINK(pp) == p);
        assert(LLINK(rb_stack.top()) == pp or RLINK(rb_stack.top()) == pp);
 
        Node * sp = LLINK(pp) == p ? RLINK(pp) : LLINK(pp);
        if (COLOR(sp) == RED)
          {
            Node *& ppp = rb_stack.top();
 
            if (LLINK(pp) == p)
              {
                sp = LLINK(sp);
                ppp = rotate_to_left_rk(pp, ppp);
              }
            else
              {
                sp = RLINK(sp);
                ppp = rotate_to_right_rk(pp, ppp);
              }
 
            COLOR(ppp) = BLACK;
            COLOR(pp) = RED;
          }
 
        Node * np, * snp;
        if (LLINK(pp) == p)
          {
            np = RLINK(sp);
            snp = LLINK(sp);
          }
        else
          {
            np = LLINK(sp);
            snp = RLINK(sp);
          }
 
        if (COLOR(np) == RED)
          {
            Node * ppp = rb_stack.top();
 
            if (RLINK(sp) == np)
              rotate_to_left_rk(pp, ppp);
            else
              rotate_to_right_rk(pp, ppp);
 
            COLOR(sp) = COLOR(pp);
            COLOR(pp) = BLACK;
            COLOR(np) = BLACK;
 
            return;
          }
 
        if (COLOR(snp) == RED)
          {
            Node * ppp = rb_stack.top();
 
            if (LLINK(sp) == snp)
              {
                rotate_to_right_rk(sp, pp);
                rotate_to_left_rk(pp, ppp);
              }
            else
              {
                rotate_to_left_rk(sp, pp);
                rotate_to_right_rk(pp, ppp);
              }
 
            COLOR(snp) = COLOR(pp);
            COLOR(pp) = BLACK;
 
            return;
          }
 
        if (COLOR(pp) == RED)
          {
            COLOR(pp) = BLACK;
            COLOR(sp) = RED;
            return;
          }
 
        COLOR(sp) = RED;
        p = pp;
        pp = rb_stack.pop();
      }
  }
 
  // Update counters along the stack after insertion
  void update_counters_after_insertion() noexcept
  {
    // Stack contains: [head, ..., nodes in path, ..., closest to insertion]
    // top(0) = closest node, top(size-1) = head (don't update)
    const size_t sz = rb_stack.size();
    for (size_t i = 0; i < sz - 1; ++i)
      ++COUNT(rb_stack.top(i));
  }
 
  // Update counters along the stack after deletion
  void update_counters_after_deletion() noexcept
  {
    const size_t sz = rb_stack.size();
    for (size_t i = 0; i < sz - 1; ++i)
      --COUNT(rb_stack.top(i));
  }
 
public:
 
  typedef Key key_type;
 
  Compare & key_comp() noexcept { return cmp; }
 
  Compare & get_compare() noexcept { return key_comp(); }
 
  Gen_Rb_Tree_Rk(Compare cmp_arg = Compare())
    : head(&head_node), root(head_node.getR()),
      rb_stack(Node::MaxHeight), cmp(cmp_arg)
  { /* empty */ }
 
  void swap(Gen_Rb_Tree_Rk & tree) noexcept
  {
    std::swap(root, tree.root);
    std::swap(cmp, tree.cmp);
  }
 
  Gen_Rb_Tree_Rk(Gen_Rb_Tree_Rk && tree) noexcept
    : head(&head_node), root(head_node.getR()),
      rb_stack(Node::MaxHeight), cmp(std::move(tree.cmp))
  {
    root = tree.root;
    tree.root = Node::NullPtr;
  }
 
  Gen_Rb_Tree_Rk & operator = (Gen_Rb_Tree_Rk && tree) noexcept
  {
    if (this != &tree)
      {
        root = tree.root;
        tree.root = Node::NullPtr;
        cmp = std::move(tree.cmp);
      }
    return *this;
  }
 
  virtual ~Gen_Rb_Tree_Rk() = default;
 
  Node * search(const Key & key)
  {
    Node * retVal = Aleph::searchInBinTree<Node, Compare>(root, key, cmp);
    return retVal == Node::NullPtr ? nullptr : retVal;
  }
 
  Node *& getRoot() noexcept { return root; }
 
  [[nodiscard]] bool is_empty() const noexcept { return root == Node::NullPtr; }
 
  [[nodiscard]] size_t size() const noexcept { return COUNT(root); }
 
  Node * insert(Node * p)
  {
    assert(p != nullptr and p != Node::NullPtr);
    assert(COLOR(p) == RED);
 
    if (root == Node::NullPtr)
      return root = p;
 
    signed char cmp_result = CmpEqual;
    Node * q = search_and_stack_rb(KEY(p), cmp_result);
    if (cmp_result == CmpLess)
      LLINK(q) = p;
    else if (cmp_result == CmpGreater)
      RLINK(q) = p;
    else
      {
        rb_stack.empty();
        return nullptr;
      }
 
    update_counters_after_insertion();
    fix_red_condition(p);
 
    return p;
  }
 
  Node * search_or_insert(Node * p)
  {
    assert(p != nullptr and p != Node::NullPtr);
    assert(COLOR(p) == RED);
 
    if (root == Node::NullPtr)
      return root = p;
 
    signed char cmp_result = CmpEqual;
    Node * q = search_and_stack_rb(KEY(p), cmp_result);
    if (cmp_result == CmpLess)
      LLINK(q) = p;
    else if (cmp_result == CmpGreater)
      RLINK(q) = p;
    else
      {
        rb_stack.empty();
        return q;
      }
 
    update_counters_after_insertion();
    fix_red_condition(p);
 
    return p;
  }
 
  Node * insert_dup(Node * p)
  {
    assert(p != nullptr and p != Node::NullPtr);
    assert(COLOR(p) == RED);
 
    if (root == Node::NullPtr)
      return root = p;
 
    signed char cmp_result = CmpEqual;
    Node * q = search_dup_and_stack_rb(KEY(p), cmp_result);
    if (cmp_result == CmpLess)
      LLINK(q) = p;
    else
      RLINK(q) = p;
 
    update_counters_after_insertion();
    fix_red_condition(p);
 
    return p;
  }
 
  [[nodiscard]] bool verify() const { return is_red_black_bst_rk(root, cmp) and check_rank_tree(root); }
 
  Node * remove(const Key & key)
  {
    if (root == Node::NullPtr)
      return nullptr;
 
    signed char cmp_result = CmpEqual;
    Node * q = search_and_stack_rb(key, cmp_result);
    if (cmp_result != CmpEqual)
      {
        rb_stack.empty();
        return nullptr;
      }
 
    Node * pq = rb_stack.top(1);
    Node * p;
 
    while (true)
      {
        if (LLINK(q) == Node::NullPtr)
          {
            if (LLINK(pq) == q)
              p = LLINK(pq) = RLINK(q);
            else
              p = RLINK(pq) = RLINK(q);
            break;
          }
 
        if (RLINK(q) == Node::NullPtr)
          {
            if (LLINK(pq) == q)
              p = LLINK(pq) = LLINK(q);
            else
              p = RLINK(pq) = LLINK(q);
            break;
          }
 
        find_succ_and_swap(q, pq);
      }
 
    update_counters_after_deletion();
 
    if (COLOR(q) == BLACK)
      fix_black_condition(p);
 
    q->reset();
    rb_stack.empty();
 
    return q;
  }
 
  Node * select(const size_t i) const
  {
    return Aleph::select(root, i);
  }
 
  std::pair<long, Node*> position(const Key & key) const noexcept
  {
    std::pair<long, Node*> ret_val;
 
    ret_val.first = BinTreeXt_Operation<Node, Compare>(cmp).
      inorder_position(root, key, ret_val.second);
 
    return ret_val;
  }
 
  std::pair<long, Node*> find_position(const Key & key) const noexcept
  {
    std::pair<long, Node*> r(-2, nullptr);
 
    r.first = BinTreeXt_Operation<Node, Compare>(cmp).
      find_position(root, key, r.second);
 
    return r;
  }
 
private:
 
  // Compute black height of RB tree (count black nodes to any leaf)
  static size_t black_height(Node * p) noexcept
  {
    size_t h = 0;
    while (p != Node::NullPtr)
      {
        if (COLOR(p) == BLACK)
          ++h;
        p = LLINK(p);  // Any path works since all paths have same black height
      }
    return h;
  }
 
  // Simple rotation without parent link update (for internal use)
  static Node * rotate_right_simple(Node * p) noexcept
  {
    Node * q = LLINK(p);
    LLINK(p) = RLINK(q);
    RLINK(q) = p;
    COUNT(p) = COUNT(LLINK(p)) + COUNT(RLINK(p)) + 1;
    COUNT(q) = COUNT(LLINK(q)) + COUNT(RLINK(q)) + 1;
    return q;
  }
 
  static Node * rotate_left_simple(Node * p) noexcept
  {
    Node * q = RLINK(p);
    RLINK(p) = LLINK(q);
    LLINK(q) = p;
    COUNT(p) = COUNT(LLINK(p)) + COUNT(RLINK(p)) + 1;
    COUNT(q) = COUNT(LLINK(q)) + COUNT(RLINK(q)) + 1;
    return q;
  }
 
  // Fix red-red violation going up from node p
  // pp_ptr is a pointer to the pointer that points to the subtree being fixed
  static void fix_red_violation(Node *& subtree_root) noexcept
  {
    // Simplified iterative fix for red-red violations
    // This version uses recursion-based fixing during join
    if (subtree_root == Node::NullPtr)
      return;
 
    // Check left child for red-red
    if (LLINK(subtree_root) != Node::NullPtr and
        COLOR(LLINK(subtree_root)) == RED)
      {
        Node * l = LLINK(subtree_root);
        if (LLINK(l) != Node::NullPtr and COLOR(LLINK(l)) == RED)
          {
            // Left-left case
            subtree_root = rotate_right_simple(subtree_root);
            COLOR(subtree_root) = BLACK;
            COLOR(RLINK(subtree_root)) = RED;
            return;
          }
        if (RLINK(l) != Node::NullPtr and COLOR(RLINK(l)) == RED)
          {
            // Left-right case
            LLINK(subtree_root) = rotate_left_simple(l);
            subtree_root = rotate_right_simple(subtree_root);
            COLOR(subtree_root) = BLACK;
            COLOR(RLINK(subtree_root)) = RED;
            return;
          }
      }
 
    // Check right child for red-red
    if (RLINK(subtree_root) != Node::NullPtr and
        COLOR(RLINK(subtree_root)) == RED)
      {
        Node * r = RLINK(subtree_root);
        if (RLINK(r) != Node::NullPtr and COLOR(RLINK(r)) == RED)
          {
            // Right-right case
            subtree_root = rotate_left_simple(subtree_root);
            COLOR(subtree_root) = BLACK;
            COLOR(LLINK(subtree_root)) = RED;
            return;
          }
        if (LLINK(r) != Node::NullPtr and COLOR(LLINK(r)) == RED)
          {
            // Right-left case
            RLINK(subtree_root) = rotate_right_simple(r);
            subtree_root = rotate_left_simple(subtree_root);
            COLOR(subtree_root) = BLACK;
            COLOR(LLINK(subtree_root)) = RED;
            return;
          }
      }
  }
 
  // Extract minimum node with rebalancing
  // Returns the extracted min and updates p to the new root
  static Node * extract_min_rb(Node *& p) noexcept
  {
    if (p == Node::NullPtr)
      return Node::NullPtr;
 
    if (LLINK(p) == Node::NullPtr)
      {
        Node * ret = p;
        p = RLINK(p);
        ret->reset();
        return ret;
      }
 
    // Use recursive approach with fix-up
    struct ExtractHelper
    {
      static Node * extract(Node *& p, bool & height_decreased) noexcept
      {
        if (LLINK(p) == Node::NullPtr)
          {
            Node * ret = p;
            height_decreased = (COLOR(p) == BLACK);
            p = RLINK(p);
            ret->reset();
            return ret;
          }
 
        bool child_decreased = false;
        Node * ret = extract(LLINK(p), child_decreased);
        --COUNT(p);
 
        if (child_decreased)
          {
            // Left subtree's black height decreased
            // Need to rebalance
            Node * s = RLINK(p);  // sibling
            if (s != Node::NullPtr)
              {
                if (COLOR(s) == RED)
                  {
                    // Case 1: sibling is red
                    p = rotate_left_simple(p);
                    COLOR(p) = BLACK;
                    COLOR(LLINK(p)) = RED;
                    // Continue fixing in LLINK(p)
                    s = RLINK(LLINK(p));
                  }
 
                if (s != Node::NullPtr)
                  {
                    if ((LLINK(s) == Node::NullPtr or COLOR(LLINK(s)) == BLACK) and
                        (RLINK(s) == Node::NullPtr or COLOR(RLINK(s)) == BLACK))
                      {
                        // Case 2: sibling and its children are black
                        COLOR(s) = RED;
                        if (COLOR(p) == RED)
                          {
                            COLOR(p) = BLACK;
                            height_decreased = false;
                          }
                        else
                          height_decreased = true;
                      }
                    else
                      {
                        // Case 3 or 4: sibling has a red child
                        if (RLINK(s) == Node::NullPtr or COLOR(RLINK(s)) == BLACK)
                          {
                            // Case 3: left child of sibling is red
                            COLOR(LLINK(s)) = BLACK;
                            COLOR(s) = RED;
                            RLINK(p) = rotate_right_simple(s);
                          }
                        // Case 4: right child of sibling is red
                        Color old_color = COLOR(p);
                        p = rotate_left_simple(p);
                        COLOR(p) = old_color;
                        COLOR(LLINK(p)) = BLACK;
                        if (RLINK(p) != Node::NullPtr)
                          COLOR(RLINK(p)) = BLACK;
                        height_decreased = false;
                      }
                  }
                else
                  height_decreased = (COLOR(p) == BLACK);
              }
            else
              height_decreased = (COLOR(p) == BLACK);
          }
        else
          height_decreased = false;
 
        return ret;
      }
    };
 
    bool dummy = false;
    return ExtractHelper::extract(p, dummy);
  }
 
  // Extract maximum node with rebalancing
  static Node * extract_max_rb(Node *& p) noexcept
  {
    if (p == Node::NullPtr)
      return Node::NullPtr;
 
    if (RLINK(p) == Node::NullPtr)
      {
        Node * ret = p;
        p = LLINK(p);
        ret->reset();
        return ret;
      }
 
    struct ExtractHelper
    {
      static Node * extract(Node *& p, bool & height_decreased) noexcept
      {
        if (RLINK(p) == Node::NullPtr)
          {
            Node * ret = p;
            height_decreased = (COLOR(p) == BLACK);
            p = LLINK(p);
            ret->reset();
            return ret;
          }
 
        bool child_decreased = false;
        Node * ret = extract(RLINK(p), child_decreased);
        --COUNT(p);
 
        if (child_decreased)
          {
            Node * s = LLINK(p);  // sibling
            if (s != Node::NullPtr)
              {
                if (COLOR(s) == RED)
                  {
                    p = rotate_right_simple(p);
                    COLOR(p) = BLACK;
                    COLOR(RLINK(p)) = RED;
                    s = LLINK(RLINK(p));
                  }
 
                if (s != Node::NullPtr)
                  {
                    if ((LLINK(s) == Node::NullPtr or COLOR(LLINK(s)) == BLACK) and
                        (RLINK(s) == Node::NullPtr or COLOR(RLINK(s)) == BLACK))
                      {
                        COLOR(s) = RED;
                        if (COLOR(p) == RED)
                          {
                            COLOR(p) = BLACK;
                            height_decreased = false;
                          }
                        else
                          height_decreased = true;
                      }
                    else
                      {
                        if (LLINK(s) == Node::NullPtr or COLOR(LLINK(s)) == BLACK)
                          {
                            COLOR(RLINK(s)) = BLACK;
                            COLOR(s) = RED;
                            LLINK(p) = rotate_left_simple(s);
                          }
                        Color old_color = COLOR(p);
                        p = rotate_right_simple(p);
                        COLOR(p) = old_color;
                        COLOR(RLINK(p)) = BLACK;
                        if (LLINK(p) != Node::NullPtr)
                          COLOR(LLINK(p)) = BLACK;
                        height_decreased = false;
                      }
                  }
                else
                  height_decreased = (COLOR(p) == BLACK);
              }
            else
              height_decreased = (COLOR(p) == BLACK);
          }
        else
          height_decreased = false;
 
        return ret;
      }
    };
 
    bool dummy = false;
    return ExtractHelper::extract(p, dummy);
  }
 
  // Join two RB trees with a pivot node
  // All keys in t1 < pivot < all keys in t2
  // bh1 and bh2 are black heights
  static Node * join_with_pivot_rb(Node * t1, size_t bh1, Node * pivot,
                                   Node * t2, size_t bh2) noexcept
  {
    if (bh1 == bh2)
      {
        // Simple case: equal black heights
        LLINK(pivot) = t1;
        RLINK(pivot) = t2;
        COLOR(pivot) = RED;
        COUNT(pivot) = COUNT(t1) + COUNT(t2) + 1;
        return pivot;
      }
 
    if (bh1 > bh2)
      {
        // t1 is taller (more black nodes), descend right spine
        return join_right_rb(t1, bh1, pivot, t2, bh2);
      }
    // t2 is taller, descend left spine
    return join_left_rb(t1, bh1, pivot, t2, bh2);
  }
 
  // Join when bh1 > bh2
  static Node * join_right_rb(Node * t1, size_t bh1, Node * pivot,
                              Node * t2, size_t bh2) noexcept
  {
    if (t1 == Node::NullPtr)
      {
        LLINK(pivot) = Node::NullPtr;
        RLINK(pivot) = t2;
        COLOR(pivot) = BLACK;
        COUNT(pivot) = COUNT(t2) + 1;
        return pivot;
      }
 
    // Descend right spine until black height matches bh2
    size_t curr_bh = bh1;
    if (COLOR(t1) == BLACK)
      --curr_bh;
 
    if (curr_bh == bh2)
      {
        // Found the join point
        LLINK(pivot) = RLINK(t1);
        RLINK(pivot) = t2;
        COLOR(pivot) = RED;
        COUNT(pivot) = COUNT(RLINK(t1)) + COUNT(t2) + 1;
        RLINK(t1) = pivot;
        COUNT(t1) = COUNT(LLINK(t1)) + COUNT(pivot) + 1;
 
        // Fix red-red if needed
        if (COLOR(t1) == RED)
          {
            // t1 is red and pivot is red - need rotation
            // Since we came from the right, do left rotation
            Node * result = rotate_left_simple(t1);
            COLOR(result) = BLACK;
            COLOR(LLINK(result)) = RED;
            return result;
          }
        return t1;
      }
 
    // Continue descending
    Node * right_result = join_right_rb(RLINK(t1), curr_bh, pivot, t2, bh2);
    RLINK(t1) = right_result;
    COUNT(t1) = COUNT(LLINK(t1)) + COUNT(RLINK(t1)) + 1;
 
    // Check for red-red violation
    if (COLOR(t1) == BLACK and RLINK(t1) != Node::NullPtr and COLOR(RLINK(t1)) == RED)
      {
        if (RLINK(RLINK(t1)) != Node::NullPtr and COLOR(RLINK(RLINK(t1))) == RED)
          {
            Node * result = rotate_left_simple(t1);
            COLOR(result) = BLACK;
            COLOR(LLINK(result)) = RED;
            COLOR(RLINK(result)) = BLACK;
            return result;
          }
        if (LLINK(RLINK(t1)) != Node::NullPtr and COLOR(LLINK(RLINK(t1))) == RED)
          {
            RLINK(t1) = rotate_right_simple(RLINK(t1));
            Node * result = rotate_left_simple(t1);
            COLOR(result) = BLACK;
            COLOR(LLINK(result)) = RED;
            COLOR(RLINK(result)) = BLACK;
            return result;
          }
      }
 
    return t1;
  }
 
  // Join when bh2 > bh1
  static Node * join_left_rb(Node * t1, size_t bh1, Node * pivot,
                             Node * t2, size_t bh2) noexcept
  {
    if (t2 == Node::NullPtr)
      {
        LLINK(pivot) = t1;
        RLINK(pivot) = Node::NullPtr;
        COLOR(pivot) = BLACK;
        COUNT(pivot) = COUNT(t1) + 1;
        return pivot;
      }
 
    size_t curr_bh = bh2;
    if (COLOR(t2) == BLACK)
      --curr_bh;
 
    if (curr_bh == bh1)
      {
        RLINK(pivot) = LLINK(t2);
        LLINK(pivot) = t1;
        COLOR(pivot) = RED;
        COUNT(pivot) = COUNT(t1) + COUNT(LLINK(t2)) + 1;
        LLINK(t2) = pivot;
        COUNT(t2) = COUNT(pivot) + COUNT(RLINK(t2)) + 1;
 
        if (COLOR(t2) == RED)
          {
            Node * result = rotate_right_simple(t2);
            COLOR(result) = BLACK;
            COLOR(RLINK(result)) = RED;
            return result;
          }
        return t2;
      }
 
    Node * left_result = join_left_rb(t1, bh1, pivot, LLINK(t2), curr_bh);
    LLINK(t2) = left_result;
    COUNT(t2) = COUNT(LLINK(t2)) + COUNT(RLINK(t2)) + 1;
 
    // Check for red-red violation
    if (COLOR(t2) == BLACK and LLINK(t2) != Node::NullPtr and COLOR(LLINK(t2)) == RED)
      {
        if (LLINK(LLINK(t2)) != Node::NullPtr and COLOR(LLINK(LLINK(t2))) == RED)
          {
            Node * result = rotate_right_simple(t2);
            COLOR(result) = BLACK;
            COLOR(LLINK(result)) = BLACK;
            COLOR(RLINK(result)) = RED;
            return result;
          }
        if (RLINK(LLINK(t2)) != Node::NullPtr and COLOR(RLINK(LLINK(t2))) == RED)
          {
            LLINK(t2) = rotate_left_simple(LLINK(t2));
            Node * result = rotate_right_simple(t2);
            COLOR(result) = BLACK;
            COLOR(LLINK(result)) = BLACK;
            COLOR(RLINK(result)) = RED;
            return result;
          }
      }
 
    return t2;
  }
 
  // Recursive join of two RB trees
  static Node * join_exclusive_rec_rb(Node * t1, size_t bh1,
                                      Node * t2, size_t bh2) noexcept
  {
    if (t1 == Node::NullPtr)
      return t2;
    if (t2 == Node::NullPtr)
      return t1;
 
    // Extract a pivot from the larger tree
    Node * pivot;
    if (bh1 >= bh2)
      {
        pivot = extract_max_rb(t1);
        if (t1 != Node::NullPtr)
          bh1 = black_height(t1);
        else
          bh1 = 0;
      }
    else
      {
        pivot = extract_min_rb(t2);
        if (t2 != Node::NullPtr)
          bh2 = black_height(t2);
        else
          bh2 = 0;
      }
 
    return join_with_pivot_rb(t1, bh1, pivot, t2, bh2);
  }
 
  // Split by key recursively
  Node * split_key_rec_rb(Node * p, const Key & key,
                          Node *& t1, Node *& t2) noexcept
  {
    if (p == Node::NullPtr)
      {
        t1 = t2 = Node::NullPtr;
        return Node::NullPtr;
      }
 
    Node * found;
    if (cmp(key, KEY(p)))
      {
        Node * left_t2;
        found = split_key_rec_rb(LLINK(p), key, t1, left_t2);
 
        LLINK(p) = Node::NullPtr;
        const size_t left_t2_bh = (left_t2 != Node::NullPtr) ? black_height(left_t2) : 0;
        const size_t right_bh = (RLINK(p) != Node::NullPtr) ? black_height(RLINK(p)) : 0;
 
        Node * right_tree = RLINK(p);
        RLINK(p) = Node::NullPtr;
        COUNT(p) = 1;
        COLOR(p) = RED;
 
        t2 = join_with_pivot_rb(left_t2, left_t2_bh, p, right_tree, right_bh);
        if (t2 != Node::NullPtr)
          COLOR(t2) = BLACK;
      }
    else if (cmp(KEY(p), key))
      {
        Node * right_t1;
        found = split_key_rec_rb(RLINK(p), key, right_t1, t2);
 
        RLINK(p) = Node::NullPtr;
        const size_t right_t1_bh = (right_t1 != Node::NullPtr) ? black_height(right_t1) : 0;
        const size_t left_bh = (LLINK(p) != Node::NullPtr) ? black_height(LLINK(p)) : 0;
 
        Node * left_tree = LLINK(p);
        LLINK(p) = Node::NullPtr;
        COUNT(p) = 1;
        COLOR(p) = RED;
 
        t1 = join_with_pivot_rb(left_tree, left_bh, p, right_t1, right_t1_bh);
        if (t1 != Node::NullPtr)
          COLOR(t1) = BLACK;
      }
    else
      {
        t1 = LLINK(p);
        t2 = RLINK(p);
        LLINK(p) = RLINK(p) = Node::NullPtr;
        COUNT(p) = 1;
        COLOR(p) = RED;
        found = p;
        if (t1 != Node::NullPtr)
          COLOR(t1) = BLACK;
        if (t2 != Node::NullPtr)
          COLOR(t2) = BLACK;
      }
 
    return found;
  }
 
  // Split by key including duplicates
  void split_key_dup_rec_rb(Node * p, const Key & key,
                            Node *& t1, Node *& t2) noexcept
  {
    if (p == Node::NullPtr)
      {
        t1 = t2 = Node::NullPtr;
        return;
      }
 
    if (cmp(key, KEY(p)))
      {
        Node * left_t2;
        split_key_dup_rec_rb(LLINK(p), key, t1, left_t2);
 
        LLINK(p) = Node::NullPtr;
        const size_t left_t2_bh = (left_t2 != Node::NullPtr) ? black_height(left_t2) : 0;
        const size_t right_bh = (RLINK(p) != Node::NullPtr) ? black_height(RLINK(p)) : 0;
 
        Node * right_tree = RLINK(p);
        RLINK(p) = Node::NullPtr;
        COUNT(p) = 1;
        COLOR(p) = RED;
 
        t2 = join_with_pivot_rb(left_t2, left_t2_bh, p, right_tree, right_bh);
        if (t2 != Node::NullPtr)
          COLOR(t2) = BLACK;
      }
    else
      {
        Node * right_t1;
        split_key_dup_rec_rb(RLINK(p), key, right_t1, t2);
 
        RLINK(p) = Node::NullPtr;
        const size_t right_t1_bh = (right_t1 != Node::NullPtr) ? black_height(right_t1) : 0;
        const size_t left_bh = (LLINK(p) != Node::NullPtr) ? black_height(LLINK(p)) : 0;
 
        Node * left_tree = LLINK(p);
        LLINK(p) = Node::NullPtr;
        COUNT(p) = 1;
        COLOR(p) = RED;
 
        t1 = join_with_pivot_rb(left_tree, left_bh, p, right_t1, right_t1_bh);
        if (t1 != Node::NullPtr)
          COLOR(t1) = BLACK;
      }
  }
 
  // Split by position recursively
  void split_pos_rec_rb(Node * p, size_t pos, Node *& t1, Node *& t2) noexcept
  {
    if (p == Node::NullPtr)
      {
        t1 = t2 = Node::NullPtr;
        return;
      }
 
    size_t left_count = COUNT(LLINK(p));
 
    if (pos <= left_count)
      {
        Node * left_t2;
        split_pos_rec_rb(LLINK(p), pos, t1, left_t2);
 
        LLINK(p) = Node::NullPtr;
        const size_t left_t2_bh = (left_t2 != Node::NullPtr) ? black_height(left_t2) : 0;
        const size_t right_bh = (RLINK(p) != Node::NullPtr) ? black_height(RLINK(p)) : 0;
 
        Node * right_tree = RLINK(p);
        RLINK(p) = Node::NullPtr;
        COUNT(p) = 1;
        COLOR(p) = RED;
 
        t2 = join_with_pivot_rb(left_t2, left_t2_bh, p, right_tree, right_bh);
        if (t2 != Node::NullPtr)
          COLOR(t2) = BLACK;
      }
    else
      {
        Node * right_t1;
        split_pos_rec_rb(RLINK(p), pos - left_count - 1, right_t1, t2);
 
        RLINK(p) = Node::NullPtr;
        const size_t right_t1_bh = (right_t1 != Node::NullPtr) ? black_height(right_t1) : 0;
        const size_t left_bh = (LLINK(p) != Node::NullPtr) ? black_height(LLINK(p)) : 0;
 
        Node * left_tree = LLINK(p);
        LLINK(p) = Node::NullPtr;
        COUNT(p) = 1;
        COLOR(p) = RED;
 
        t1 = join_with_pivot_rb(left_tree, left_bh, p, right_t1, right_t1_bh);
        if (t1 != Node::NullPtr)
          COLOR(t1) = BLACK;
      }
  }
 
public:
 
  void join_exclusive(Gen_Rb_Tree_Rk & t) noexcept
  {
    if (t.root == Node::NullPtr)
      return;
 
    if (root == Node::NullPtr)
      {
        root = t.root;
        t.root = Node::NullPtr;
        return;
      }
 
    // Collect nodes from t in preorder and insert them one by one
    // This is O(m log(n+m)) but guarantees correctness
    FixedStack<Node*> stack(Node::MaxHeight);
    stack.push(t.root);
    t.root = Node::NullPtr;
 
    while (not stack.is_empty())
      {
        Node * p = stack.pop();
        Node * left = LLINK(p);
        Node * right = RLINK(p);
 
        // Reset node and insert
        p->reset();
        insert(p);
 
        if (right != Node::NullPtr)
          stack.push(right);
        if (left != Node::NullPtr)
          stack.push(left);
      }
  }
 
  Node * split_key(const Key & key, Gen_Rb_Tree_Rk & t1,
                   Gen_Rb_Tree_Rk & t2) noexcept
  {
    if (root == Node::NullPtr)
      return nullptr;
 
    // Simple O(n) implementation: iterate through tree and partition
    Node * found = nullptr;
    FixedStack<Node*> stack(Node::MaxHeight);
    stack.push(root);
    root = Node::NullPtr;
 
    while (not stack.is_empty())
      {
        Node * p = stack.pop();
        Node * left = LLINK(p);
        Node * right = RLINK(p);
 
        if (right != Node::NullPtr)
          stack.push(right);
        if (left != Node::NullPtr)
          stack.push(left);
 
        p->reset();
 
        if (cmp(KEY(p), key))
          t1.insert(p);
        else if (cmp(key, KEY(p)))
          t2.insert(p);
        else
          found = p;  // Found the key
      }
 
    return found;
  }
 
  void split_key_dup(const Key & key, Gen_Rb_Tree_Rk & t1,
                     Gen_Rb_Tree_Rk & t2) noexcept
  {
    if (root == Node::NullPtr)
      return;
 
    FixedStack<Node*> stack(Node::MaxHeight);
    stack.push(root);
    root = Node::NullPtr;
 
    while (not stack.is_empty())
      {
        Node * p = stack.pop();
        Node * left = LLINK(p);
        Node * right = RLINK(p);
 
        if (right != Node::NullPtr)
          stack.push(right);
        if (left != Node::NullPtr)
          stack.push(left);
 
        p->reset();
 
        if (cmp(key, KEY(p)))
          t2.insert(p);
        else
          t1.insert_dup(p);
      }
  }
 
  void split_pos(size_t pos, Gen_Rb_Tree_Rk & t1,
                 Gen_Rb_Tree_Rk & t2) noexcept
  {
    if (root == Node::NullPtr)
      return;
 
    if (pos == 0)
      {
        t2.root = root;
        root = Node::NullPtr;
        return;
      }
 
    if (pos >= size())
      {
        t1.root = root;
        root = Node::NullPtr;
        return;
      }
 
    // Simple O(n) implementation using inorder traversal
    size_t count = 0;
    FixedStack<Node*> stack(Node::MaxHeight);
    Node * curr = root;
    root = Node::NullPtr;
 
    // Inorder traversal
    while (curr != Node::NullPtr or not stack.is_empty())
      {
        while (curr != Node::NullPtr)
          {
            stack.push(curr);
            Node * left = LLINK(curr);
            LLINK(curr) = Node::NullPtr;  // Disconnect
            curr = left;
          }
 
        curr = stack.pop();
        Node * right = RLINK(curr);
        curr->reset();
 
        if (count < pos)
          t1.insert(curr);
        else
          t2.insert(curr);
 
        ++count;
        curr = right;
      }
  }
 
  class Iterator : public BinTreeXt_Iterator<Gen_Rb_Tree_Rk, Node, Key, Compare>
  {
    using Base = BinTreeXt_Iterator<Gen_Rb_Tree_Rk, Node, Key, Compare>;
 
  public:
 
    using Base::Base;
    using Base::operator=;
  }; // end class Iterator
};
 
 
template <typename Key, class Compare = Aleph::less<Key>>
struct Rb_Tree_Rk : public Gen_Rb_Tree_Rk<RbNodeRk, Key, Compare>
{
  using Base = Gen_Rb_Tree_Rk<RbNodeRk, Key, Compare>;
  using Base::Base;
};
 
 
template <typename Key, class Compare = Aleph::less<Key>>
struct Rb_Tree_Rk_Vtl : public Gen_Rb_Tree_Rk<RbNodeRkVtl, Key, Compare>
{
  using Base = Gen_Rb_Tree_Rk<RbNodeRkVtl, Key, Compare>;
  using Base::Base;
};
 
 
} // end namespace Aleph
 
# endif // TPL_RBRK_H