stl_algobase.h

stl_algobase.h
// Filename:    stl_algobase.h

// Comment By:  凝霜
// E-mail:      mdl2009@vip.qq.com
// Blog:        http://blog.csdn.net/mdl13412

// 这个文件中定义的都是一些最常用的算法, 我仅仅给出一个思路,
// 不进行详尽讲解, 具体算法请参考算法书籍, 推荐《算法导论》
// 另外, 对于基础薄弱的, 推荐《大话数据结构》, 此书我读了一下
// 试读章节, 适合初学者学习

/*
 *
 * 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.
 *
 *
 * Copyright (c) 1996
 * 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.
 */

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

#ifndef __SGI_STL_INTERNAL_ALGOBASE_H
#define __SGI_STL_INTERNAL_ALGOBASE_H

#ifndef __STL_CONFIG_H
#include <stl_config.h>
#endif
#ifndef __SGI_STL_INTERNAL_RELOPS
#include <stl_relops.h>
#endif
#ifndef __SGI_STL_INTERNAL_PAIR_H
#include <stl_pair.h>
#endif
#ifndef __TYPE_TRAITS_H_
#include <type_traits.h>
#endif

#include <string.h>
#include <limits.h>
#include <stdlib.h>
#include <stddef.h>
#include <new.h>
#include <iostream.h>

#ifndef __SGI_STL_INTERNAL_ITERATOR_H
#include <stl_iterator.h>
#endif

__STL_BEGIN_NAMESPACE

// 第三个参数为什么为指针参见<stl_iterator.h>
template <class ForwardIterator1, class ForwardIterator2, class T>
inline void __iter_swap(ForwardIterator1 a, ForwardIterator2 b, T*)
{
  // 这里交换的其实是内部对象
  T tmp = *a;
  *a = *b;
  *b = tmp;
}

template <class ForwardIterator1, class ForwardIterator2>
inline void iter_swap(ForwardIterator1 a, ForwardIterator2 b)
{
  // 型别以第一个为准
  __iter_swap(a, b, value_type(a));
}

// 进行交换操作, 使用的是operator =()
template <class T>
inline void swap(T& a, T& b)
{
  T tmp = a;
  a = b;
  b = tmp;
}

#ifndef __BORLANDC__

#undef min
#undef max

// max和min非常简单了, 由于返回的是引用, 因此可以嵌套使用
template <class T>
inline const T& min(const T& a, const T& b)
{
  return b < a ? b : a;
}

template <class T>
inline const T& max(const T& a, const T& b)
{
  return  a < b ? b : a;
}

#endif /* __BORLANDC__ */

template <class T, class Compare>
inline const T& min(const T& a, const T& b, Compare comp)
{
  return comp(b, a) ? b : a;
}

template <class T, class Compare>
inline const T& max(const T& a, const T& b, Compare comp)
{
  return comp(a, b) ? b : a;
}

// 这是不支持随机访问的情况
template <class InputIterator, class OutputIterator>
inline OutputIterator __copy(InputIterator first, InputIterator last,
                             OutputIterator result, input_iterator_tag)
{
  // first != last导致要进行迭代器的比较, 效率低
  for ( ; first != last; ++result, ++first)
    *result = *first;
  return result;
}

template <class RandomAccessIterator, class OutputIterator, class Distance>
inline OutputIterator
__copy_d(RandomAccessIterator first, RandomAccessIterator last,
         OutputIterator result, Distance*)
{
  // 不进行迭代器间的比较, 直接指定循环次数, 高效
  for (Distance n = last - first; n > ; --n, ++result, ++first)
    *result = *first;
  return result;
}

// 这是支持随机访问的情况
template <class RandomAccessIterator, class OutputIterator>
inline OutputIterator
__copy(RandomAccessIterator first, RandomAccessIterator last,
       OutputIterator result, random_access_iterator_tag)
{
  return __copy_d(first, last, result, distance_type(first));
}

template <class InputIterator, class OutputIterator>
struct __copy_dispatch
{
  // 这里是一个仿函数. 再次派发
  OutputIterator operator()(InputIterator first, InputIterator last,
                            OutputIterator result) {
    return __copy(first, last, result, iterator_category(first));
  }
};

// 提供兼容
#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION

// 可以直接移动, 不需要额外操作
template <class T>
inline T* __copy_t(const T* first, const T* last, T* result, __true_type)
{
  memmove(result, first, sizeof(T) * (last - first));
  return result + (last - first);
}

// 需要进行一些处理, 保证对象复制的正确性
template <class T>
inline T* __copy_t(const T* first, const T* last, T* result, __false_type)
{
  return __copy_d(first, last, result, (ptrdiff_t*) );
}

// 对指针提供特化
template <class T>
struct __copy_dispatch<T*, T*>
{
  T* operator()(T* first, T* last, T* result)
  {
    // 判断其内部是否具有trivial_assignment_operator, 以进行派发
    typedef typename __type_traits<T>::has_trivial_assignment_operator t;
    return __copy_t(first, last, result, t());
  }
};

template <class T>
struct __copy_dispatch<const T*, T*>
{
  T* operator()(const T* first, const T* last, T* result) {
    typedef typename __type_traits<T>::has_trivial_assignment_operator t;
    return __copy_t(first, last, result, t());
  }
};

#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */

// 将[first, last)拷贝到result处
template <class InputIterator, class OutputIterator>
inline OutputIterator copy(InputIterator first, InputIterator last,
                           OutputIterator result)
{
  // 此处进行函数派发操作
  return __copy_dispatch<InputIterator,OutputIterator>()(first, last, result);
}

// 针对char字符串的特化, 效率至上, C++的设计理念
inline char* copy(const char* first, const char* last, char* result)
{
  memmove(result, first, last - first);
  return result + (last - first);
}

// 针对wchar_t字符串的特化, 效率至上, C++的设计理念
inline wchar_t* copy(const wchar_t* first, const wchar_t* last,
                     wchar_t* result) {
  memmove(result, first, sizeof(wchar_t) * (last - first));
  return result + (last - first);
}

template <class BidirectionalIterator1, class BidirectionalIterator2>
inline BidirectionalIterator2 __copy_backward(BidirectionalIterator1 first,
                                              BidirectionalIterator1 last,
                                              BidirectionalIterator2 result)
{
  while (first != last) *--result = *--last;
  return result;
}

template <class BidirectionalIterator1, class BidirectionalIterator2>
struct __copy_backward_dispatch
{
  BidirectionalIterator2 operator()(BidirectionalIterator1 first,
                                    BidirectionalIterator1 last,
                                    BidirectionalIterator2 result)
  {
    return __copy_backward(first, last, result);
  }
};

#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION

template <class T>
inline T* __copy_backward_t(const T* first, const T* last, T* result,
                            __true_type)
{
  const ptrdiff_t N = last - first;
  memmove(result - N, first, sizeof(T) * N);
  return result - N;
}

template <class T>
inline T* __copy_backward_t(const T* first, const T* last, T* result,
                            __false_type)
{
  return __copy_backward(first, last, result);
}

template <class T>
struct __copy_backward_dispatch<T*, T*>
{
  T* operator()(T* first, T* last, T* result)
  {
    typedef typename __type_traits<T>::has_trivial_assignment_operator t;
    return __copy_backward_t(first, last, result, t());
  }
};

template <class T>
struct __copy_backward_dispatch<const T*, T*>
{
  T* operator()(const T* first, const T* last, T* result)
  {
    typedef typename __type_traits<T>::has_trivial_assignment_operator t;
    return __copy_backward_t(first, last, result, t());
  }
};

#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */

// 将[first, last)的元素反向拷贝到(..., last)处, 其机制和copy非常接近, 不做说明
template <class BidirectionalIterator1, class BidirectionalIterator2>
inline BidirectionalIterator2 copy_backward(BidirectionalIterator1 first,
                                            BidirectionalIterator1 last,
                                            BidirectionalIterator2 result)
{
  return __copy_backward_dispatch<BidirectionalIterator1,
                                  BidirectionalIterator2>()(first, last,
                                                            result);
}

template <class InputIterator, class Size, class OutputIterator>
pair<InputIterator, OutputIterator> __copy_n(InputIterator first, Size count,
                                             OutputIterator result,
                                             input_iterator_tag)
{
  for ( ; count > ; --count, ++first, ++result)
    *result = *first;
  return pair<InputIterator, OutputIterator>(first, result);
}

template <class RandomAccessIterator, class Size, class OutputIterator>
inline pair<RandomAccessIterator, OutputIterator>
__copy_n(RandomAccessIterator first, Size count,
         OutputIterator result,
         random_access_iterator_tag)
{
  // 使用copy()以选择最高效的拷贝算法
  RandomAccessIterator last = first + count;
  return pair<RandomAccessIterator, OutputIterator>(last,
                                                    copy(first, last, result));
}

// 从first拷贝n个值到result处
template <class InputIterator, class Size, class OutputIterator>
inline pair<InputIterator, OutputIterator>
copy_n(InputIterator first, Size count,
       OutputIterator result)
{
  // 进行函数派发, 选咋高效版本
  return __copy_n(first, count, result, iterator_category(first));
}

// 使用value填充[first, last)区间
template <class ForwardIterator, class T>
void fill(ForwardIterator first, ForwardIterator last, const T& value)
{
  for ( ; first != last; ++first)
    *first = value;     // 调用的是operator =(), 这个要特别注意
}

// 用value填充[first, first + n)的区间
// 为了防止越界, 可以使用下面实例的技巧
// vector<int> vec();
// for (int i = 0; i < 10; ++i)
//      vec.push_back(i);
// fill_n(inserter(iv, iv.begin()), 100, 10);   // 这就可以使容器动态扩展
template <class OutputIterator, class Size, class T>
OutputIterator fill_n(OutputIterator first, Size n, const T& value)
{
  for ( ; n > ; --n, ++first)
    *first = value;
  return first;
}

// 找到两个序列第一个失配的地方, 结果以pair返回
template <class InputIterator1, class InputIterator2>
pair<InputIterator1, InputIterator2> mismatch(InputIterator1 first1,
                          InputIterator1 last1,
                          InputIterator2 first2)
{
  // 遍历区间, 寻找失配点
  while (first1 != last1 && *first1 == *first2) {
    ++first1;
    ++first2;
  }
  return pair<InputIterator1, InputIterator2>(first1, first2);
}

// 提供用户自定义的二元判别式, 其余同上
template <class InputIterator1, class InputIterator2, class BinaryPredicate>
pair<InputIterator1, InputIterator2> mismatch(InputIterator1 first1,
                          InputIterator1 last1,
                          InputIterator2 first2,
                          BinaryPredicate binary_pred)
{
  while (first1 != last1 && binary_pred(*first1, *first2)) {
    ++first1;
    ++first2;
  }
  return pair<InputIterator1, InputIterator2>(first1, first2);
}

// 如果序列在[first, last)内相等, 则返回true, 如果第二个序列有多余的元素,
// 则不进行比较, 直接忽略. 如果第二个序列元素不足, 会导致未定义行为
template <class InputIterator1, class InputIterator2>
inline bool equal(InputIterator1 first1, InputIterator1 last1,
          InputIterator2 first2)
{
  for ( ; first1 != last1; ++first1, ++first2)
    if (*first1 != *first2)     // 只要有一个不相等就判定为false
      return false;
  return true;
}

// 进行比较的操作改为用户指定的二元判别式, 其余同上
template <class InputIterator1, class InputIterator2, class BinaryPredicate>
inline bool equal(InputIterator1 first1, InputIterator1 last1,
          InputIterator2 first2, BinaryPredicate binary_pred)
{
  for ( ; first1 != last1; ++first1, ++first2)
    if (!binary_pred(*first1, *first2))
      return false;
  return true;
}

// 字典序比较, 非常类似字符串的比较
// 具体比较方式参见STL文档, 另外strcmp()也可以参考
template <class InputIterator1, class InputIterator2>
bool lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
                 InputIterator2 first2, InputIterator2 last2)
{
  for ( ; first1 != last1 && first2 != last2; ++first1, ++first2) {
    if (*first1 < *first2)
      return true;
    if (*first2 < *first1)
      return false;
  }
  return first1 == last1 && first2 != last2;
}

// 二元判别式自己指定, 其余同上
template <class InputIterator1, class InputIterator2, class Compare>
bool lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
                 InputIterator2 first2, InputIterator2 last2,
                 Compare comp) {
  for ( ; first1 != last1 && first2 != last2; ++first1, ++first2)
  {
    if (comp(*first1, *first2))
      return true;
    if (comp(*first2, *first1))
      return false;
  }
  return first1 == last1 && first2 != last2;
}

// 针对字符串的特化, 效率至上
inline bool
lexicographical_compare(const unsigned char* first1,
                        const unsigned char* last1,
                        const unsigned char* first2,
                        const unsigned char* last2)
{
  const size_t len1 = last1 - first1;
  const size_t len2 = last2 - first2;
  const int result = memcmp(first1, first2, min(len1, len2));
  return result !=  ? result <  : len1 < len2;
}

// 针对字符串的特化, 效率至上
inline bool lexicographical_compare(const char* first1, const char* last1,
                                    const char* first2, const char* last2)
{
#if CHAR_MAX == SCHAR_MAX
  return lexicographical_compare((const signed char*) first1,
                                 (const signed char*) last1,
                                 (const signed char*) first2,
                                 (const signed char*) last2);
#else
  return lexicographical_compare((const unsigned char*) first1,
                                 (const unsigned char*) last1,
                                 (const unsigned char*) first2,
                                 (const unsigned char*) last2);
#endif
}

// 一句话概括, 这个是strcmp()的泛化版本
template <class InputIterator1, class InputIterator2>
int lexicographical_compare_3way(InputIterator1 first1, InputIterator1 last1,
                                 InputIterator2 first2, InputIterator2 last2)
{
  while (first1 != last1 && first2 != last2) {
    if (*first1 < *first2) return -;
    if (*first2 < *first1) return ;
    ++first1; ++first2;
  }
  if (first2 == last2) {
    return !(first1 == last1);
  } else {
    return -;
  }
}

// 特换版本, 效率决定一切
inline int
lexicographical_compare_3way(const unsigned char* first1,
                             const unsigned char* last1,
                             const unsigned char* first2,
                             const unsigned char* last2)
{
  const ptrdiff_t len1 = last1 - first1;
  const ptrdiff_t len2 = last2 - first2;
  const int result = memcmp(first1, first2, min(len1, len2));
  return result !=  ? result : (len1 == len2 ?  : (len1 < len2 ? - : ));
}

inline int lexicographical_compare_3way(const char* first1, const char* last1,
                                        const char* first2, const char* last2)
{
#if CHAR_MAX == SCHAR_MAX
  return lexicographical_compare_3way(
                (const signed char*) first1,
                                (const signed char*) last1,
                                (const signed char*) first2,
                                (const signed char*) last2);
#else
  return lexicographical_compare_3way((const unsigned char*) first1,
                                      (const unsigned char*) last1,
                                      (const unsigned char*) first2,
                                      (const unsigned char*) last2);
#endif
}

__STL_END_NAMESPACE

#endif /* __SGI_STL_INTERNAL_ALGOBASE_H */

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// mode:C++
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