STL中，关联式容器的内部结构是一颗平衡二叉树，以便获得良好的搜索效率。红黑树是平衡二叉树的一种，它不像AVL树那样要求绝对平衡，降低了对旋转的要求，但是其性能并没有下降很多，它的搜索、插入、删除都能以O(nlogn)时间完成。平衡可以在一次或者两次旋转解决，是“性价比”很高的平衡二叉树。

RB-tree(red black tree)红黑树是平衡二叉树。它满足一下规则

（1）每个节点不是红色就是黑色。
（2）根节点是黑色。
（3）如果节点为红色，则其子节点比为黑色。
（4）任何一个节点到NULL（树尾端）的路径上，所含的黑色节点数必须相同。
根据上面的规则（4），新添加的节点必须为红色，否则到NULL路径上黑色节点会增加。
根据上面的规则（3），新添加节点的父节点必须为黑色，因为新添加节点必须为红色。
当新的节点根据二叉树的搜索规则到达插入点时，未能满足上面两条，就必须调整颜色并旋转树形。
为了方便讨论插入新节点，定义几个代名词：
假设新节点为X，其父节点为P，其祖父节点为G，伯父节点（父节点之兄弟节点）为S，曾祖父节点为GG。现在根据红黑树规则4，X必须为红色；若P为红色（违反了规则3,需调整），G必须为黑色。于是，根据X的插入位置和外围节点（S和GG）的颜色，分以下四种情况：
（1）S为黑色且X为外侧插入。对此种情况，我们先对P，G做一次单旋转，再更改P，G颜色，即可重新满足红黑树规则3。如下图


（2）S为黑色且X为内侧插入。对此情况，先对P，X做一次单旋转并更改G，X颜色，再将结果对G做一次单旋转，即可满足红黑树性质3。如下图5


（3）S为红色且X为外侧插入。先对P和G做一次单旋转，并改变X的颜色。此时如果GG为黑色，则搞定。如下图。否则见情况（4）

（4）S为红色且X为外侧插入。先对P和G做一次单旋转，并改变X的颜色。此时如果GG为黑色，还要持续网上做，直到不再有父子连续为红的情况。如下图

G++ 2.91.57，cygnus\cygwin-b20\include\g++\stl_tree.h 完整列表
/*
 *
 * Copyright (c) 1996,1997
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 */

/* NOTE: This is an internal header file, included by other STL headers.
 *   You should not attempt to use it directly.
 */

#ifndef __SGI_STL_INTERNAL_TREE_H
#define __SGI_STL_INTERNAL_TREE_H


/*
这章讲解Red-black tree（红黑树）class，用来当做SLT关系容器（如set，multiset，map，
multimap）。里面所用的insertion和deletion方法以Cormen, Leiserson 和 Riveset所著的
《Introduction to Algorithms》一书为基础，但是有以下两点不同:

(1)header不仅指向root，也指向红黑树的最左节点，以便用常数时间实现begin()，并且也指向红黑树的最右边节点，以便
set相关泛型算法（如set_union等等）可以有线性时间实现。
(2)当一个即将被删除的节点有两个孩子节点时，它的successor（后继）node is relinked into its place, ranther than copied,
如此一来唯一失效的（invalidated）的迭代器就只是那些referring to the deleted node.
*/
#include <stl_algobase.h>
#include <stl_alloc.h>
#include <stl_construct.h>
#include <stl_function.h>

__STL_BEGIN_NAMESPACE 
//定义红色黑色。红色为0，黑色为1
typedef bool __rb_tree_color_type;
const __rb_tree_color_type __rb_tree_red = false;
const __rb_tree_color_type __rb_tree_black = true;
//红黑树Base类
struct __rb_tree_node_base
{
  typedef __rb_tree_color_type color_type;
  typedef __rb_tree_node_base* base_ptr;

  color_type color; 	// 节点颜色，红或者黑
  base_ptr parent;  	// RB树的许多操作，必须知道其父结点
  base_ptr left;	  	// 指向左孩子节点。
  base_ptr right;   	// 指向右孩子节点。

  static base_ptr minimum(base_ptr x)
  {
    while (x->left != 0) x = x->left;	// 一直向左走，就会找到最小值
    return x;							// 这是二叉查找树的性质。同理下面的函数
  }

  static base_ptr maximum(base_ptr x)
  {
    while (x->right != 0) x = x->right;
    return x;
  }
};

//红黑树类，继承Base类
template <class Value>
struct __rb_tree_node : public __rb_tree_node_base
{
  typedef __rb_tree_node<Value>* link_type;//指向节点的指针
  Value value_field;	// 节点的值
};
//迭代器基类,类型为bidirectional_iterator_tag，可以双向移动
struct __rb_tree_base_iterator
{
  typedef __rb_tree_node_base::base_ptr base_ptr;//指向红黑树节点指针
  typedef bidirectional_iterator_tag iterator_category;
  typedef ptrdiff_t difference_type;

  //指向红黑树节点的指针，用它来和容器产生关系
  base_ptr node;

  // 以下其實可實作於 operator++ 內，因為再無他處會呼叫此函式了。
  /*
	重载运算符++和--。目的是找到前驱和后继节点。
	关于前驱和后继节点的定义，类似二叉查找树。可以在这里找到：
	http://blog.csdn.net/kangroger/article/details/8774121
  */
  //下面只是为了实现oprerator++的，其他地方不会调用了。
  //++是找到其后继节点
  void increment()
  {
	//如果有右孩子，就是找右子树的最小值
    if (node->right != 0) {		// 如果有右孩子
      node = node->right;		// 就向右走
      while (node->left != 0)	// 然后向左走到底
        node = node->left;		
    }
	//如果无右子树。那么就找其最低祖先节点，且这个最低祖先节点的左孩子节点
	//也是其祖先节点（每个节点就是自己的祖先节点）
    else {					// 没有右孩子
      base_ptr y = node->parent;	// 找出父节点
      while (node == y->right) {	// 如果现行节点本身是个右子节点
        node = y;				// 就一直上溯，直到「不为右子节点」止。
        y = y->parent;
      }
	  /*
		若此时的右子节点不等于此时的父节点,此时的父节点即为解答,否则此时的node为解答.
		这样做是为了应付一种特殊情况：我们欲寻找根节点的下一个节点。而恰巧根节点无右孩子。
		当然，以上特殊做法必须配合RB-tree根节点与特殊header之间的特殊关系
	  */
      if (node->right != y)		// 若此时的右子节点不等于此时的父节点
        node = y;				// 此时的父节点即为解答
                                      // 否则此时的node为解答
    }						
  
  }

  // 以下其實可實作於 operator-- 內，因為再無他處會呼叫此函式了。
  /*
	查找前驱结点。
  */
  void decrement()
  {
    if (node->color == __rb_tree_red &&	// 如果是红节点，且
        node->parent->parent == node)		// 父节点的父节点等于自己
      node = node->right;				// 狀況(1) 右子节点即为解答。
	  /*
	  以上情况发生于node为header时（亦即node为end()时）。注意，header之右孩子即
	  mostright，指向整棵树的max节点。
	  */
	//左子树的最大值结点
    else if (node->left != 0) {	
      base_ptr y = node->left;
      while (y->right != 0)	
        y = y->right;	
      node = y;		
    }
	/*
	既非根节点，且无左子树。找其最低祖先节点y，且y的右孩子也是其祖先节点
	*/
    else {							
      base_ptr y = node->parent;			//找出父节点
      while (node == y->left) {	
        node = y;					
        y = y->parent;	
      }
      node = y;
    }
  }
};
//此处为迭代器
template <class Value, class Ref, class Ptr>
struct __rb_tree_iterator : public __rb_tree_base_iterator
{
  typedef Value value_type;
  typedef Ref reference;
  typedef Ptr pointer;
  typedef __rb_tree_iterator<Value, Value&, Value*>     iterator;
  typedef __rb_tree_iterator<Value, const Value&, const Value*> const_iterator;
  typedef __rb_tree_iterator<Value, Ref, Ptr>   self;
  typedef __rb_tree_node<Value>* link_type;

  //几个构造函数
  __rb_tree_iterator() {}
  __rb_tree_iterator(link_type x) { node = x; }
  __rb_tree_iterator(const iterator& it) { node = it.node; }

  //重载操作符
  reference operator*() const { return link_type(node)->value_field; }
#ifndef __SGI_STL_NO_ARROW_OPERATOR
  pointer operator->() const { return &(operator*()); }
#endif /* __SGI_STL_NO_ARROW_OPERATOR */

	//++做了封装，调用的是increment()
  self& operator++() { increment(); return *this; }
  self operator++(int) {
    self tmp = *this;
    increment();
    return tmp;
  }
    //调用的是decrement
  self& operator--() { decrement(); return *this; }
  self operator--(int) {
    self tmp = *this;
    decrement();
    return tmp;
  }
};
//两个迭代器相等，意味着它们指向同一个红黑树节点
inline bool operator==(const __rb_tree_base_iterator& x,
                       const __rb_tree_base_iterator& y) {
  return x.node == y.node;
}

inline bool operator!=(const __rb_tree_base_iterator& x,
                       const __rb_tree_base_iterator& y) {
  return x.node != y.node;
}

#ifndef __STL_CLASS_PARTIAL_SPECIALIZATION
//返回迭代器类型
inline bidirectional_iterator_tag
iterator_category(const __rb_tree_base_iterator&) {
  return bidirectional_iterator_tag();
}

inline __rb_tree_base_iterator::difference_type*
distance_type(const __rb_tree_base_iterator&) {
  return (__rb_tree_base_iterator::difference_type*) 0;
}

template <class Value, class Ref, class Ptr>
inline Value* value_type(const __rb_tree_iterator<Value, Ref, Ptr>&) {
  return (Value*) 0;
}

#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */

// 以下都是全域函式：__rb_tree_rotate_left(), __rb_tree_rotate_right(),
// __rb_tree_rebalance(), __rb_tree_rebalance_for_erase()

/*
新节点必须为红色节点。如果安插处的父节点为红色，就违反了红黑色规则（3）。此时要旋转和改变颜色
*/
//左旋转
inline void 
__rb_tree_rotate_left(__rb_tree_node_base* x, __rb_tree_node_base*& root)
{
  // x 为旋转点
  __rb_tree_node_base* y = x->right;	// y为x的右孩子
  x->right = y->left;
  if (y->left !=0)
    y->left->parent = x;		// 不要忘了回马枪设置父节点
  y->parent = x->parent;

  // 令 y 完全顶替 x 的地位（必须将x对其父节点的关系完全接收过来）
  if (x == root)					// x 为根节点
    root = y;
  else if (x == x->parent->left)	// x 为父节点的左孩子
    x->parent->left = y;
  else							// x 为父节点的右孩子
    x->parent->right = y;			
  y->left = x;
  x->parent = y;
}

//右旋转
inline void 
__rb_tree_rotate_right(__rb_tree_node_base* x, __rb_tree_node_base*& root)
{
  // x 为旋转点
  __rb_tree_node_base* y = x->left;	// y x的左孩子
  x->left = y->right;
  if (y->right != 0)
    y->right->parent = x; 	// 別忘了回马枪设置父节点
  y->parent = x->parent;

  // 令 y 完全顶替 x 的地位（必须将x对其父节点的关系完全接收过来）
  if (x == root)					// x 为根节点
    root = y;
  else if (x == x->parent->right)	// x 为父节点的右孩子
    x->parent->right = y;
  else							// x 为父节点的左孩子
    x->parent->left = y;
  y->right = x;
  x->parent = y;
}


//重新令RB-tree平衡（改变颜色和旋转）参数x为新增节点，参数二为root节点
inline void 
__rb_tree_rebalance(__rb_tree_node_base* x, __rb_tree_node_base*& root)
{
  x->color = __rb_tree_red;		// 新节点比为红色
  while (x != root && x->parent->color == __rb_tree_red) { // 父节点为红色
    if (x->parent == x->parent->parent->left) { // 父节点为祖父节点的左孩子
      __rb_tree_node_base* y = x->parent->parent->right;	// 令y 为伯父节点
      if (y && y->color == __rb_tree_red) { 		// 伯父节点存在，且为红色
        x->parent->color = __rb_tree_black;  		// 更改父节点为黑色
        y->color = __rb_tree_black;				// 更改伯父节点为黑色
        x->parent->parent->color = __rb_tree_red; 	// 更改祖父节点为红色
        x = x->parent->parent;
      }
      else {	// 无伯父节点或伯父节点为黑色（NULL就是黑色）
        if (x == x->parent->right) { // 新增节点为父节点的右孩子
          x = x->parent;
          __rb_tree_rotate_left(x, root); // 第一个参数为左旋转点
        }
        x->parent->color = __rb_tree_black;	// 改变颜色，父节点为黑色
        x->parent->parent->color = __rb_tree_red;
        __rb_tree_rotate_right(x->parent->parent, root); // 第一参数为右旋转点
      }
    }
    else {	// 父节点为祖父节点的右孩子
      __rb_tree_node_base* y = x->parent->parent->left; // y为伯父节点
      if (y && y->color == __rb_tree_red) {		// 有伯父节点且为红色
        x->parent->color = __rb_tree_black;		// 更改父节点为黑色
        y->color = __rb_tree_black; 				// 更改伯父节点为黑色
        x->parent->parent->color = __rb_tree_red; 	// 更改祖父节点为红色
        x = x->parent->parent;	// 准备继续往上层检查……
      }
      else {	// 无伯父节点或伯父节点为黑色（NULL就是黑色）
        if (x == x->parent->left) {	// 新节点为父节点的左孩子
          x = x->parent;
          __rb_tree_rotate_right(x, root); 	// 第一个参数右旋转
        }
        x->parent->color = __rb_tree_black;	// 改变颜色，父节点为黑色
        x->parent->parent->color = __rb_tree_red;
        __rb_tree_rotate_left(x->parent->parent, root); // 第一个参数做旋转
      }
    }
  }	// while 結束
  root->color = __rb_tree_black;	// 根节点永远为黑色
}
//删除结点z
inline __rb_tree_node_base*
__rb_tree_rebalance_for_erase(__rb_tree_node_base* z,
                              __rb_tree_node_base*& root,
                              __rb_tree_node_base*& leftmost,
                              __rb_tree_node_base*& rightmost)
{
  __rb_tree_node_base* y = z;
  __rb_tree_node_base* x = 0;
  __rb_tree_node_base* x_parent = 0;
  if (y->left == 0)             // z has at most one non-null child. y == z.
    x = y->right;               // x might be null.
  else
    if (y->right == 0)          // z has exactly one non-null child.  y == z.
      x = y->left;              // x is not null.
    else {                      // z has two non-null children.  Set y to
      y = y->right;             //   z's successor.  x might be null.
      while (y->left != 0)
        y = y->left;
      x = y->right;
    }
  if (y != z) {                 // relink y in place of z.  y is z's successor
    z->left->parent = y; 
    y->left = z->left;
    if (y != z->right) {
      x_parent = y->parent;
      if (x) x->parent = y->parent;
      y->parent->left = x;      // y must be a left child
      y->right = z->right;
      z->right->parent = y;
    }
    else
      x_parent = y;  
    if (root == z)
      root = y;
    else if (z->parent->left == z)
      z->parent->left = y;
    else 
      z->parent->right = y;
    y->parent = z->parent;
    __STD::swap(y->color, z->color);
    y = z;
    // y now points to node to be actually deleted
  }
  else {                        // y == z
    x_parent = y->parent;
    if (x) x->parent = y->parent;   
    if (root == z)
      root = x;
    else 
      if (z->parent->left == z)
        z->parent->left = x;
      else
        z->parent->right = x;
    if (leftmost == z) 
      if (z->right == 0)        // z->left must be null also
        leftmost = z->parent;
    // makes leftmost == header if z == root
      else
        leftmost = __rb_tree_node_base::minimum(x);
    if (rightmost == z)  
      if (z->left == 0)         // z->right must be null also
        rightmost = z->parent;  
    // makes rightmost == header if z == root
      else                      // x == z->left
        rightmost = __rb_tree_node_base::maximum(x);
  }
  if (y->color != __rb_tree_red) { 
    while (x != root && (x == 0 || x->color == __rb_tree_black))
      if (x == x_parent->left) {
        __rb_tree_node_base* w = x_parent->right;
        if (w->color == __rb_tree_red) {
          w->color = __rb_tree_black;
          x_parent->color = __rb_tree_red;
          __rb_tree_rotate_left(x_parent, root);
          w = x_parent->right;
        }
        if ((w->left == 0 || w->left->color == __rb_tree_black) &&
            (w->right == 0 || w->right->color == __rb_tree_black)) {
          w->color = __rb_tree_red;
          x = x_parent;
          x_parent = x_parent->parent;
        } else {
          if (w->right == 0 || w->right->color == __rb_tree_black) {
            if (w->left) w->left->color = __rb_tree_black;
            w->color = __rb_tree_red;
            __rb_tree_rotate_right(w, root);
            w = x_parent->right;
          }
          w->color = x_parent->color;
          x_parent->color = __rb_tree_black;
          if (w->right) w->right->color = __rb_tree_black;
          __rb_tree_rotate_left(x_parent, root);
          break;
        }
      } else {                  // same as above, with right <-> left.
        __rb_tree_node_base* w = x_parent->left;
        if (w->color == __rb_tree_red) {
          w->color = __rb_tree_black;
          x_parent->color = __rb_tree_red;
          __rb_tree_rotate_right(x_parent, root);
          w = x_parent->left;
        }
        if ((w->right == 0 || w->right->color == __rb_tree_black) &&
            (w->left == 0 || w->left->color == __rb_tree_black)) {
          w->color = __rb_tree_red;
          x = x_parent;
          x_parent = x_parent->parent;
        } else {
          if (w->left == 0 || w->left->color == __rb_tree_black) {
            if (w->right) w->right->color = __rb_tree_black;
            w->color = __rb_tree_red;
            __rb_tree_rotate_left(w, root);
            w = x_parent->left;
          }
          w->color = x_parent->color;
          x_parent->color = __rb_tree_black;
          if (w->left) w->left->color = __rb_tree_black;
          __rb_tree_rotate_right(x_parent, root);
          break;
        }
      }
    if (x) x->color = __rb_tree_black;
  }
  return y;
}

template <class Key, class Value, class KeyOfValue, class Compare,
          class Alloc = alloc>
class rb_tree {
protected:
  typedef void* void_pointer;
  typedef __rb_tree_node_base* base_ptr;
  typedef __rb_tree_node<Value> rb_tree_node;
  typedef simple_alloc<rb_tree_node, Alloc> rb_tree_node_allocator;
  typedef __rb_tree_color_type color_type;
public:
  //这里没有定义iterator，在后面定义
  typedef Key key_type;
  typedef Value value_type;
  typedef value_type* pointer;
  typedef const value_type* const_pointer;
  typedef value_type& reference;
  typedef const value_type& const_reference;
  typedef rb_tree_node* link_type;
  typedef size_t size_type;
  typedef ptrdiff_t difference_type;
protected:
  link_type get_node() { return rb_tree_node_allocator::allocate(); }
  void put_node(link_type p) { rb_tree_node_allocator::deallocate(p); }

  link_type create_node(const value_type& x) {
    link_type tmp = get_node();			// 配置空间
    __STL_TRY {
      construct(&tmp->value_field, x);	// 构建内容
    }
    __STL_UNWIND(put_node(tmp));
    return tmp;
  }

  link_type clone_node(link_type x) {	// 复制一个节点（值和颜色）
    link_type tmp = create_node(x->value_field);
    tmp->color = x->color;
    tmp->left = 0;
    tmp->right = 0;
    return tmp;
  }

  void destroy_node(link_type p) {
    destroy(&p->value_field);		// 析构
    put_node(p);					// 释放空间
  }

protected:
  // RB-tree 只以三个资料表现
  size_type node_count; // 追踪记录树的大小（节点总数）
  link_type header;  
  Compare key_compare;	 // 节点的键值比较判断准则。是个函数 function object。

  //以下三个函数用来方便取得header的成员
  link_type& root() const { return (link_type&) header->parent; }
  link_type& leftmost() const { return (link_type&) header->left; }
  link_type& rightmost() const { return (link_type&) header->right; }

  //以下六个函数用来方便取得节点x的成员。x为函数参数
  static link_type& left(link_type x) { return (link_type&)(x->left); }
  static link_type& right(link_type x) { return (link_type&)(x->right); }
  static link_type& parent(link_type x) { return (link_type&)(x->parent); }
  static reference value(link_type x) { return x->value_field; }
  static const Key& key(link_type x) { return KeyOfValue()(value(x)); }
  static color_type& color(link_type x) { return (color_type&)(x->color); }

  //和上面六个作用相同，注意x参数类型不同。一个是基类指针，一个是派生类指针
  static link_type& left(base_ptr x) { return (link_type&)(x->left); }
  static link_type& right(base_ptr x) { return (link_type&)(x->right); }
  static link_type& parent(base_ptr x) { return (link_type&)(x->parent); }
  static reference value(base_ptr x) { return ((link_type)x)->value_field; }
  static const Key& key(base_ptr x) { return KeyOfValue()(value(link_type(x)));} 
  static color_type& color(base_ptr x) { return (color_type&)(link_type(x)->color); }

  //找最大值和最小值。node class 有这个功能函数
  static link_type minimum(link_type x) { 
    return (link_type)  __rb_tree_node_base::minimum(x);
  }
  static link_type maximum(link_type x) {
    return (link_type) __rb_tree_node_base::maximum(x);
  }

public:
  typedef __rb_tree_iterator<value_type, reference, pointer> iterator;
  typedef __rb_tree_iterator<value_type, const_reference, const_pointer> 
          const_iterator;

#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION
  typedef reverse_iterator<const_iterator> const_reverse_iterator;
  typedef reverse_iterator<iterator> reverse_iterator;
#else /* __STL_CLASS_PARTIAL_SPECIALIZATION */
  typedef reverse_bidirectional_iterator<iterator, value_type, reference,
                                         difference_type>
          reverse_iterator; 
  typedef reverse_bidirectional_iterator<const_iterator, value_type,
                                         const_reference, difference_type>
          const_reverse_iterator;
#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */ 
private:
  iterator __insert(base_ptr x, base_ptr y, const value_type& v);
  link_type __copy(link_type x, link_type p);
  void __erase(link_type x);
  void init() {
    header = get_node();	// 产生一个节点空间，令header指向它
    color(header) = __rb_tree_red; // 令 header 尾红色，用來区 header  
                                   // 和 root（在 iterator.operator++ 中）
    root() = 0;
    leftmost() = header;	// 令 header 的左孩子为自己。
    rightmost() = header;	// 令 header 的右孩子为自己。
  }
public:
     //默认构造函数                           // allocation/deallocation
  rb_tree(const Compare& comp = Compare())
    : node_count(0), key_compare(comp) { init(); }

  // 以另一个 rb_tree  x 初始化
  rb_tree(const rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& x) 
    : node_count(0), key_compare(x.key_compare)
  { 
    header = get_node();	
    color(header) = __rb_tree_red;	
    if (x.root() == 0) {	//  如果 x 空树
      root() = 0;
      leftmost() = header; 
      rightmost() = header; 
    }
    else {	//  x 不是空树
      __STL_TRY {
        root() = __copy(x.root(), header);		// 拷贝红黑树x 
      }
      __STL_UNWIND(put_node(header));
      leftmost() = minimum(root());	// 令 header 的左孩子为最小节点
      rightmost() = maximum(root());	// 令 header 的右孩子为最大节点
    }
    node_count = x.node_count;
  }
  ~rb_tree() {
    clear();
    put_node(header);
  }
  rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& 
  operator=(const rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& x);

public:    
                                // accessors:
  Compare key_comp() const { return key_compare; }
  iterator begin() { return leftmost(); }		// RB 树的起始为最左（最小节点）
  const_iterator begin() const { return leftmost(); }
  iterator end() { return header; }	// RB 树的终节点为header所指处
  const_iterator end() const { return header; }
  reverse_iterator rbegin() { return reverse_iterator(end()); }
  const_reverse_iterator rbegin() const { 
    return const_reverse_iterator(end()); 
  }
  reverse_iterator rend() { return reverse_iterator(begin()); }
  const_reverse_iterator rend() const { 
    return const_reverse_iterator(begin());
  } 
  bool empty() const { return node_count == 0; }
  size_type size() const { return node_count; }
  size_type max_size() const { return size_type(-1); }

  void swap(rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& t) {

	//RB-tree只有三个资料表现成员，所以两颗RB-tree互换时，只需互换3个成员
    __STD::swap(header, t.header);
    __STD::swap(node_count, t.node_count);
    __STD::swap(key_compare, t.key_compare);
  }
    
public:
                                // insert/erase
  // 将 x 安插到 RB-tree 中（保持节点值独一无二）。
  pair<iterator,bool> insert_unique(const value_type& x);
  // 将 x 安插到 RB-tree 中（允许重复节点）
  iterator insert_equal(const value_type& x);

  iterator insert_unique(iterator position, const value_type& x);
  iterator insert_equal(iterator position, const value_type& x);

#ifdef __STL_MEMBER_TEMPLATES  
  template <class InputIterator>
  void insert_unique(InputIterator first, InputIterator last);
  template <class InputIterator>
  void insert_equal(InputIterator first, InputIterator last);
#else /* __STL_MEMBER_TEMPLATES */
  void insert_unique(const_iterator first, const_iterator last);
  void insert_unique(const value_type* first, const value_type* last);
  void insert_equal(const_iterator first, const_iterator last);
  void insert_equal(const value_type* first, const value_type* last);
#endif /* __STL_MEMBER_TEMPLATES */

  void erase(iterator position);
  size_type erase(const key_type& x);
  void erase(iterator first, iterator last);
  void erase(const key_type* first, const key_type* last);
  void clear() {
    if (node_count != 0) {
      __erase(root());
      leftmost() = header;
      root() = 0;
      rightmost() = header;
      node_count = 0;
    }
  }      

public:
                                // 集合（set）的各种操作行为
  iterator find(const key_type& x);
  const_iterator find(const key_type& x) const;
  size_type count(const key_type& x) const;
  iterator lower_bound(const key_type& x);
  const_iterator lower_bound(const key_type& x) const;
  iterator upper_bound(const key_type& x);
  const_iterator upper_bound(const key_type& x) const;
  pair<iterator,iterator> equal_range(const key_type& x);
  pair<const_iterator, const_iterator> equal_range(const key_type& x) const;

public:
                                // Debugging.
  bool __rb_verify() const;
};

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
inline bool operator==(const rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& x, 
                       const rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& y) {
  return x.size() == y.size() && equal(x.begin(), x.end(), y.begin());
}
//重载<运算符，使用的是STL泛型算法<span style="font-family: Arial, Helvetica, sans-serif;">lexicographical_compare</span>
template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
inline bool operator<(const rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& x, 
                      const rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& y) {
  return lexicographical_compare(x.begin(), x.end(), y.begin(), y.end());
}

#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
inline void swap(rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& x, 
                 rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& y) {
  x.swap(y);
}

#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */

//重载赋值运算符=
template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& 
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::
operator=(const rb_tree<Key, Value, KeyOfValue, Compare, Alloc>& x) {
  if (this != &x) {//防止自身赋值
                                // Note that Key may be a constant type.
    clear();//先清除
    node_count = 0;
    key_compare = x.key_compare;        
    if (x.root() == 0) {
      root() = 0;
      leftmost() = header;
      rightmost() = header;
    }
    else {
      root() = __copy(x.root(), header);
      leftmost() = minimum(root());
      rightmost() = maximum(root());
      node_count = x.node_count;
    }
  }
  return *this;
}

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::iterator
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::
__insert(base_ptr x_, base_ptr y_, const Value& v) {
//参数x_为新值安插点，参数y_为安插点之父节点，参数v 为新值
  link_type x = (link_type) x_;
  link_type y = (link_type) y_;
  link_type z;

  //key_compare是键值得比较准则，是个函数或函数指针
  if (y == header || x != 0 || key_compare(KeyOfValue()(v), key(y))) {
    z = create_node(v);  // 产生一个新节点
    left(y) = z;          // 这使得当y为header时，leftmost()=z
    if (y == header) {
      root() = z;
      rightmost() = z;
    }
    else if (y == leftmost())	// 如果y为最左节点
      leftmost() = z;           	// 维护leftmost()，使它永远指向最左节点
  }
  else {
    z = create_node(v);
    right(y) = z;				// 令新节点成为安插点之父节点y的右孩子
    if (y == rightmost())
      rightmost() = z;          	// 维护rightmost()，使它永远指向最右节点
  }
  parent(z) = y;		// 设定新节点的父节点
  left(z) = 0;		// 设定新孩子节点的左孩子
  right(z) = 0; 		// 设定新孩子节点的右孩子
                          // 新节点的颜色将在 __rb_tree_rebalance() 设定并调整
  __rb_tree_rebalance(z, header->parent);	// 参数一为新增节点，参数二为root
  ++node_count;		// 节点数增加
  return iterator(z);	// 返回迭代器，指向新增节点
}

// 安插新值；允许键值重复。返回新插入节点的迭代器
template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::iterator
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::insert_equal(const Value& v)
{
  link_type y = header;
  link_type x = root();	 
  while (x != 0) {		// 从根节点开始，向下寻找适当安插位置
    y = x;
    x = key_compare(KeyOfValue()(v), key(x)) ? left(x) : right(x);
  }
  return __insert(x, y, v);
}

/*
不允许键值重复，否则安插无效。
返回值是个pair，第一个元素是个RB-tree迭代器，指向新增节点。
第二个元素表示安插是否成功。
*/
template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
pair<typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::iterator, bool>
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::insert_unique(const Value& v)
{
  link_type y = header;
  link_type x = root();
  bool comp = true;
  while (x != 0) { 		// 从根节点开始向下寻找适当安插位置
    y = x;
    comp = key_compare(KeyOfValue()(v), key(x)); // v 键值小于目前节点的键值？
    x = comp ? left(x) : right(x);	// 遇「大」往左，遇「小于或等于」往右
  }
  //离开while循环之后，y所指即为安插点的父节点，x必为叶子节点

  iterator j = iterator(y);   // 令迭代器j指向安插点之父节点 y
  if (comp)	//如果离开while循环时comp为真，表示 父节点键值>v ，将安插在左孩子处
    if (j == begin())   // 如果j是最左节点
      return pair<iterator,bool>(__insert(x, y, v), true);
      // 以上，x 为安插点，y 为安插点之父节点，v 为新值。
    else	// 否则（安插点之父节点不是最左节点）
      --j;	// 调整 j，回头准备测试...
  if (key_compare(key(j.node), KeyOfValue()(v)))	
    // 小于新值（表示遇「小」，将安插于右侧）
    return pair<iterator,bool>(__insert(x, y, v), true);

  //若运行到这里，表示键值有重复，不应该插入
  return pair<iterator,bool>(j, false);
}


template <class Key, class Val, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Val, KeyOfValue, Compare, Alloc>::iterator 
rb_tree<Key, Val, KeyOfValue, Compare, Alloc>::insert_unique(iterator position,
                                                             const Val& v) {
  if (position.node == header->left) // begin()
    if (size() > 0 && key_compare(KeyOfValue()(v), key(position.node)))
      return __insert(position.node, position.node, v);
  // first argument just needs to be non-null 
    else
      return insert_unique(v).first;
  else if (position.node == header) // end()
    if (key_compare(key(rightmost()), KeyOfValue()(v)))
      return __insert(0, rightmost(), v);
    else
      return insert_unique(v).first;
  else {
    iterator before = position;
    --before;
    if (key_compare(key(before.node), KeyOfValue()(v))
        && key_compare(KeyOfValue()(v), key(position.node)))
      if (right(before.node) == 0)
        return __insert(0, before.node, v); 
      else
        return __insert(position.node, position.node, v);
    // first argument just needs to be non-null 
    else
      return insert_unique(v).first;
  }
}

template <class Key, class Val, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Val, KeyOfValue, Compare, Alloc>::iterator 
rb_tree<Key, Val, KeyOfValue, Compare, Alloc>::insert_equal(iterator position,
                                                            const Val& v) {
  if (position.node == header->left) // begin()
    if (size() > 0 && key_compare(KeyOfValue()(v), key(position.node)))
      return __insert(position.node, position.node, v);
  // first argument just needs to be non-null 
    else
      return insert_equal(v);
  else if (position.node == header) // end()
    if (!key_compare(KeyOfValue()(v), key(rightmost())))
      return __insert(0, rightmost(), v);
    else
      return insert_equal(v);
  else {
    iterator before = position;
    --before;
    if (!key_compare(KeyOfValue()(v), key(before.node))
        && !key_compare(key(position.node), KeyOfValue()(v)))
      if (right(before.node) == 0)
        return __insert(0, before.node, v); 
      else
        return __insert(position.node, position.node, v);
    // first argument just needs to be non-null 
    else
      return insert_equal(v);
  }
}

#ifdef __STL_MEMBER_TEMPLATES  

template <class K, class V, class KoV, class Cmp, class Al> template<class II>
void rb_tree<K, V, KoV, Cmp, Al>::insert_equal(II first, II last) {
  for ( ; first != last; ++first)
    insert_equal(*first);
}

template <class K, class V, class KoV, class Cmp, class Al> template<class II>
void rb_tree<K, V, KoV, Cmp, Al>::insert_unique(II first, II last) {
  for ( ; first != last; ++first)
    insert_unique(*first);
}

#else /* __STL_MEMBER_TEMPLATES */

template <class K, class V, class KoV, class Cmp, class Al>
void
rb_tree<K, V, KoV, Cmp, Al>::insert_equal(const V* first, const V* last) {
  for ( ; first != last; ++first)
    insert_equal(*first);
}

template <class K, class V, class KoV, class Cmp, class Al>
void
rb_tree<K, V, KoV, Cmp, Al>::insert_equal(const_iterator first,
                                          const_iterator last) {
  for ( ; first != last; ++first)
    insert_equal(*first);
}

template <class K, class V, class KoV, class Cmp, class A>
void 
rb_tree<K, V, KoV, Cmp, A>::insert_unique(const V* first, const V* last) {
  for ( ; first != last; ++first)
    insert_unique(*first);
}

template <class K, class V, class KoV, class Cmp, class A>
void 
rb_tree<K, V, KoV, Cmp, A>::insert_unique(const_iterator first,
                                          const_iterator last) {
  for ( ; first != last; ++first)
    insert_unique(*first);
}

#endif /* __STL_MEMBER_TEMPLATES */
         
template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
inline void
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::erase(iterator position) {
  link_type y = (link_type) __rb_tree_rebalance_for_erase(position.node,
                                                          header->parent,
                                                          header->left,
                                                          header->right);
  destroy_node(y);
  --node_count;
}

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::size_type 
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::erase(const Key& x) {
  pair<iterator,iterator> p = equal_range(x);
  size_type n = 0;
  distance(p.first, p.second, n);
  erase(p.first, p.second);
  return n;
}
//复制x到p
template <class K, class V, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<K, V, KeyOfValue, Compare, Alloc>::link_type 
rb_tree<K, V, KeyOfValue, Compare, Alloc>::__copy(link_type x, link_type p) {
                                // structural copy.  x and p must be non-null.
  link_type top = clone_node(x);
  top->parent = p;
 
  __STL_TRY {
    if (x->right)
      top->right = __copy(right(x), top);
    p = top;
    x = left(x);

    while (x != 0) {
      link_type y = clone_node(x);
      p->left = y;
      y->parent = p;
      if (x->right)
        y->right = __copy(right(x), y);
      p = y;
      x = left(x);
    }
  }
  __STL_UNWIND(__erase(top));

  return top;
}

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
void rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::__erase(link_type x) {
                                // erase without rebalancing
  while (x != 0) {
    __erase(right(x));
    link_type y = left(x);
    destroy_node(x);
    x = y;
  }
}

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
void rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::erase(iterator first, 
                                                            iterator last) {
  if (first == begin() && last == end())
    clear();
  else
    while (first != last) erase(first++);
}

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
void rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::erase(const Key* first, 
                                                            const Key* last) {
  while (first != last) erase(*first++);
}

//查找RB树中是否有键值为k的节点
template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::iterator 
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::find(const Key& k) {
  link_type y = header;        // Last node which is not less than k. 
  link_type x = root();        // Current node. 

  while (x != 0) 
    // key_compare 是 function object。
    if (!key_compare(key(x), k)) 
      // 运行到这里，表示x键值大于k。遇到大值就向左走。
      y = x, x = left(x);	// 注意语法!逗号表达式
    else
      // 运行到这里，表示x键值小于k。遇到小值就向右走。
      x = right(x);

  iterator j = iterator(y);   
  return (j == end() || key_compare(k, key(j.node))) ? end() : j;
}


template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::const_iterator 
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::find(const Key& k) const {
  link_type y = header; /* Last node which is not less than k. */
  link_type x = root(); /* Current node. */

  while (x != 0) {
   
    if (!key_compare(key(x), k))
      y = x, x = left(x);	
    else
      x = right(x);
  }
  const_iterator j = const_iterator(y);   
  return (j == end() || key_compare(k, key(j.node))) ? end() : j;
}

//计算RB树中键值为k的节点的个数
template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::size_type 
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::count(const Key& k) const {
  pair<const_iterator, const_iterator> p = equal_range(k);
  size_type n = 0;
  distance(p.first, p.second, n);
  return n;
}

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::iterator 
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::lower_bound(const Key& k) {
  link_type y = header; /* Last node which is not less than k. */
  link_type x = root(); /* Current node. */

  while (x != 0) 
    if (!key_compare(key(x), k))
      y = x, x = left(x);
    else
      x = right(x);

  return iterator(y);
}

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::const_iterator 
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::lower_bound(const Key& k) const {
  link_type y = header; /* Last node which is not less than k. */
  link_type x = root(); /* Current node. */

  while (x != 0) 
    if (!key_compare(key(x), k))
      y = x, x = left(x);
    else
      x = right(x);

  return const_iterator(y);
}

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::iterator 
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::upper_bound(const Key& k) {
  link_type y = header; /* Last node which is greater than k. */
  link_type x = root(); /* Current node. */

   while (x != 0) 
     if (key_compare(k, key(x)))
       y = x, x = left(x);
     else
       x = right(x);

   return iterator(y);
}

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::const_iterator 
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::upper_bound(const Key& k) const {
  link_type y = header; /* Last node which is greater than k. */
  link_type x = root(); /* Current node. */

   while (x != 0) 
     if (key_compare(k, key(x)))
       y = x, x = left(x);
     else
       x = right(x);

   return const_iterator(y);
}

template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
inline pair<typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::iterator,
            typename rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::iterator>
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::equal_range(const Key& k) {
  return pair<iterator, iterator>(lower_bound(k), upper_bound(k));
}

template <class Key, class Value, class KoV, class Compare, class Alloc>
inline pair<typename rb_tree<Key, Value, KoV, Compare, Alloc>::const_iterator,
            typename rb_tree<Key, Value, KoV, Compare, Alloc>::const_iterator>
rb_tree<Key, Value, KoV, Compare, Alloc>::equal_range(const Key& k) const {
  return pair<const_iterator,const_iterator>(lower_bound(k), upper_bound(k));
}

//计算从 node 至 root路径中的黑节点数量
inline int __black_count(__rb_tree_node_base* node, __rb_tree_node_base* root)
{
  if (node == 0)
    return 0;
  else {
    int bc = node->color == __rb_tree_black ? 1 : 0;
    if (node == root)
      return bc;
    else
      return bc + __black_count(node->parent, root); // 累加
  }
}

//验证己身这棵树是否符合RB树条件
template <class Key, class Value, class KeyOfValue, class Compare, class Alloc>
bool 
rb_tree<Key, Value, KeyOfValue, Compare, Alloc>::__rb_verify() const
{
  // 空树，符合RB树标准
  if (node_count == 0 || begin() == end())
    return node_count == 0 && begin() == end() &&
      header->left == header && header->right == header;

  //最左（叶）节点至 root 路径的黑节点个数
  int len = __black_count(leftmost(), root()); 
  //一下走访整个RB树，针对每个节点（从最小奥最大）……
  for (const_iterator it = begin(); it != end(); ++it) { 
    link_type x = (link_type) it.node; // __rb_tree_base_iterator::node
    link_type L = left(x);		// 这是左子节点
    link_type R = right(x); 	// 这是右子节点

    if (x->color == __rb_tree_red)
      if ((L && L->color == __rb_tree_red) ||
          (R && R->color == __rb_tree_red))
        return false;	// 父子节点同为红色，不合符RB树要求

    if (L && key_compare(key(x), key(L))) // 当前节点的键值小于左孩子节点的键值
      return false;         	// 不符合二叉查找树的要求
    if (R && key_compare(key(R), key(x))) // 当前节点的键值大于右孩子节点的键值
      return false;		// 不符合二叉查找树的要求

	//[叶子结点到root]路径内的黑色节点数，与[最左节点至root]路径内的黑色节点不同。不符合RB树要求
    if (!L && !R && __black_count(x, root()) != len) 
      return false;
  }

  if (leftmost() != __rb_tree_node_base::minimum(root()))
    return false;	// 最左节点不为最小节点，不符合二叉查找树的要求。
  if (rightmost() != __rb_tree_node_base::maximum(root()))
    return false;	// 最右节点不为最大节点，不符不符合二叉查找树的要求。

  return true;
}

__STL_END_NAMESPACE 

#endif /* __SGI_STL_INTERNAL_TREE_H */

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