动手实现自己的 STL 容器《2》---- list

1. 序：

   本文参考了侯捷的 《STL 源码分析》一书，出于兴趣，自行实现了简单的 list 容器。

   学习了 STL 的 list 容器的源代码，确实能够提高写链表代码的能力。其中的 sort 函数，可谓是非常神奇。。。

2. 实现的细节

   STL 的 list 容器采用了一个带有尾节点的环状双向链表。 如下图所示：

// Last Update:2014-04-20 18:39:47
/**
 * @file my_list.h
 * @brief a simple list
 * @author [email protected]
 * @version 0.1.00
 * @date 2014-04-18
 */

#ifndef MY_LIST_H
#define MY_LIST_H

#include <iostream>
#include <cstddef>
#include <cassert>

/**
 * list node
 */
template<class T>
struct list_node
{
  typedef list_node<T>* pointer;
  pointer prev;
  pointer next;
  T data;
};

/**
 * list's iterator
 * users can use it to iteratate over this list container
 */
template<class T>
struct list_iterator
{
  typedef T value_type;
  typedef size_t size_type;
  typedef ptrdiff_t difference_type;
  typedef T* pointer;
  typedef const T* const_pointer;
  typedef T& reference;
  typedef const T& const_reference;
  typedef list_iterator iterator;

  list_iterator(list_node<T> *p = NULL) : node(p) {}

  reference operator*() { return node->data; }
  iterator& operator++(){ 
    node = node->next;
    return *this;
  }
  iterator operator++(int){
    iterator tmp = *this;
    ++*this;
    return tmp;
  }
  iterator& operator--(){
    node = node->prev;
    return *this;
  }
  iterator operator--(int){
    iterator tmp = *this;
    --*this;
    return tmp;
  }
  bool operator==(const iterator &rhs){
    return node == rhs.node;
  }
  bool operator!=(const iterator &rhs){
    return node != rhs.node; }

  list_node<T> *node;
};

/**
 * a simple list container
 */
template<class T>
class MyList
{
public:
  typedef T value_type;
  typedef size_t size_type;
  typedef ptrdiff_t difference_type;
  typedef list_iterator<T> iterator;
  typedef const list_iterator<T> const_iterator;
  typedef T& reference;
  typedef const T& const_reference;
  typedef list_node<T>* link_type;

  MyList();
  MyList(size_type n, T value = T());
  //template<class InputIterator>
  //MyList(InputIterator first, InputIterator last);
  
  // copy control
  MyList(const MyList&);
  MyList& operator=(const MyList&);
  ~MyList();

  bool empty() const { return node->next == node;}
  difference_type size() const;

  iterator begin() {return iterator(node->next);}
  iterator end() {return iterator(node);}
  iterator begin() const {return iterator(node->next);}
  iterator end() const {return iterator(node);}
  iterator rbegin() {return iterator(node->prev);}
  iterator rbegin() const {return iterator(node->prev);}

  iterator insert(iterator position, const T& x);

  void swap(MyList& );
  void push_back(const T& x);
  void pop_back() { 
    iterator tmp = end();
    erase(--tmp);
  }

  void push_front(const T& x);
  void pop_front() {erase(begin());}

  void reverse();
  void merge(MyList &);
  void sort();

  void remove(const T&x);
  iterator erase(iterator position);
  void clear();

  void splice(iterator position, MyList& x) {
    if(!x.empty()){
      transfer(x.begin(), x.end());
    }
  }

  void splice(iterator position, MyList&, iterator i){
    iterator j = i;
    ++ j;
    if (position == i || position == j) return;
    transfer(position, i, j);
  }

  void splice(iterator position, MyList&, iterator first, iterator last) {
    if(first != last){
      transfer(position, first, last);
    }
  }

  void print();
protected:
  list_node<T> *node;
  static std::allocator<list_node<T> > alloc;

  link_type get_node(){
    link_type p = alloc.allocate(1);
    return p;
  }

  void put_node(link_type p){
    alloc.deallocate(p, 1);
  }

  link_type create_node(const T& x){
    link_type p = get_node();
    new (&p->data) T(x);
    return p;
  }

  void destroy_node(link_type p){
    (&p->data)->~T();
    put_node(p);
  }

  void empty_initialize(){
    node = get_node();
    node->prev = node;
    node->next = node;
  }

  void transfer(iterator position, iterator first, iterator last);
};

template<class T>
std::allocator<list_node<T> > MyList<T>::alloc;

template<class T>
MyList<T>::MyList()
{
  empty_initialize();
}

template<class T>
MyList<T>::MyList(size_type n, T value)
{
  empty_initialize();
  for(size_type i(0); i!=n; ++i)
    insert(begin(), value);
}

template<class T>
void MyList<T>::clear()
{
  link_type p = node->next;
  link_type next(NULL);

  while(p != node){
    next = p->next;
    destroy_node(p);
    p = next;
  }
  node->prev = node;
  node->next = node;
}

template<class T>
MyList<T>::~MyList()
{
  clear();
  destroy_node(node);
  node = NULL;
}

//copy control
template<class T>
MyList<T>::MyList(const MyList &rhs)
{
  empty_initialize();
  for(iterator it = rhs.begin(); it != rhs.end(); ++it)
    insert(end(), *it);
}

template<class T>
MyList<T>& MyList<T>::operator=(const MyList &rhs)
{
  clear();
  for(iterator it = rhs.begin(); it != rhs.end(); ++it)
    insert(end(), *it);
  return *this;
}

template<class T>
typename MyList<T>::difference_type MyList<T>::size() const
{
  difference_type len(0);
  link_type p = node->next;
  for(; p != node; p = p->next, ++len);
  return len;
}

template<class T>
typename MyList<T>::iterator MyList<T>::insert(iterator position, const T& x)
{
  link_type new_node = create_node(x);

  new_node->next = position.node;
  new_node->prev = position.node->prev;
  position.node->prev->next = new_node;
  position.node->prev = new_node;

  return iterator(new_node);
}

template<class T>
inline void MyList<T>::push_back(const T& x)
{
  insert(end(), x);
}

template<class T>
inline void MyList<T>::push_front(const T& x)
{
  insert(begin(), x);
}

template<class T>
typename MyList<T>::iterator MyList<T>::erase(iterator position)
{
  link_type next_node = link_type(position.node->next);
  link_type prev_node = link_type(position.node->prev);

  prev_node->next = next_node;
  next_node->prev = prev_node;
  destroy_node(position.node);

  return iterator(next_node);
}

// remove all nodes equal to x
template<class T>
void MyList<T>::remove(const T& x)
{
  link_type prev_node(node);
  link_type cur(node->next);
  link_type next_node(NULL);

  while(cur != node)
  {
    if(cur->data == x){
      /* delete node */
      next_node = cur->next;
      prev_node->next = next_node;
      next_node->prev = prev_node;

      destroy_node(cur);
      cur = next_node;
    }
    else{
      prev_node = cur;
      cur = cur->next;
    }
  }
}

/**
 * move [first, last) ahead of position
 * an auxillary function 
 */
template<class T>
void MyList<T>::transfer(iterator position, iterator first, iterator last)
{ 
  if(position != last)
  {
    link_type first_node = first.node;
    link_type rear_node = last.node->prev;

    //separate [first, last) from their list
    first_node->prev->next = last.node;
    last.node->prev = first_node->prev;

    //add [first, last)
    first_node->prev = position.node->prev;
    rear_node->next = position.node;
    position.node->prev->next = first_node;
    position.node->prev = rear_node;
  }
}

template<class T>
void MyList<T>::swap(MyList &rhs)
{
  if(this->node != rhs.node){
    link_type tmp = node; 
    node = rhs.node;
    rhs.node = tmp;
  }
}

template<class T>
void MyList<T>::reverse()
{ 
  /* length == 0 || length == 1*/
  if(node->next == node || node->next->next == node)
    return;
  iterator first = begin(), old(NULL); 
  ++ first;
  while(first != end()){
    old = first;
    ++ first;
    transfer(begin(), old, first);
  }
}

template<class T>
void MyList<T>::merge(MyList &x)
{
  iterator first1 = this->begin();
  iterator last1 = this->end();
  iterator first2 = x.begin();
  iterator last2 = x.end();

  // *this and x are sorted incrementally
  while(first1 != last1 && first2 != last2)
  {
    if(*first2 < *first1) {
      iterator next = first2;
      transfer(first1, first2, ++next); 
      first2 = next;
    }
    else
      ++first1;
  }
  if(first2 != last2) {
    transfer(end(), first2, last2);
  }
  assert(x.empty());
}

template<class T>
void MyList<T>::print()
{
  iterator cur = begin();
  while(cur != end())
  {
    std::cout << *cur << " ";
    ++ cur;
  }
  std::cout << std::endl;
}

/**
 * interesting sort function for list
 * std::sort is not fit for list
 * which requires random iterator
 */
template<class T>
void MyList<T>::sort()
{ 
  /* length == 0 || length == 1*/
  if(node->next == node || node->next->next == node)
    return;

  MyList<T> carry;
  MyList<T> counter[64];
  int fill = 0;
  while(!empty())
  {
    /* carry get the first node */
    carry.splice(carry.begin(), *this, begin()); 

    int i = 0;
    while(i < fill && !counter[i].empty())
    {
      counter[i].merge(carry);
      carry.swap(counter[i++]);
    }
    carry.swap(counter[i]);
    if(i == fill) ++fill;
  }

  for(int i=1; i<fill; ++i)
    counter[i].merge(counter[i-1]);
  swap(counter[fill-1]);
}

#endif  /*MY_LIST_H*/