stl源码剖析 详细学习笔记 算法(1)

//---------------------------15/03/27----------------------------

//算法

{

/*

质变算法：会改变操作对象之值

所有的stl算法都作用在由迭代器[first,last)所标示出来的区间上。质变算法
就是

运算过程会更改区间内的元素内容

非质变算法：和质变算法相反

*/

/*

stl算法的一般形式

1>所有的泛型算法的前两个参数都是一对迭代器，通常称为first和last，用以标示算法的操作区间

2>stl习惯采用前闭后开区间，写成[first,last)，表示区间包含first到last(不包含last)

之间的所有元素。

*/

//****************************数值算法*****************************

//accumulate

//把区间中的数都 “加到” init的副本中
最后返回init副本值

template<class InputIterator,
class T>

T accumulate(InputIterator first, InputIterator last, T init)

{

for(;first != last; ++first)

init = init + *first;

return init;

}

template<class InputIterator,class T,
class BinaryOperation>

T accumulate(InputIterator first, InputIterator last, T init,

BinaryOperation binary_op)

{

for(;first != last; ++first)

init = binary_op(init, *first);

return init;

}

//adjacent_difference

//把区间中的数都  “减去”
前一个数 并把结果输出到一个迭代器中

template<class InputIterator,
class OutputIterator>

OutputIterator adjacent_difference(InputIterator first, InputIterator last,

OutputIterator result)

{

if(first == last)
return result;

*result = *first;

return __adjacent_difference(first, last, result, value_type(first));

}

template<class InputIterator,
class OutputIterator,class T>

OutputIterator __adjacent_difference(InputIterator first, InputIterator last,

OutputIterator result, T*)

{

T value = *first;

while(++first != last)

{

T tmp = *first;

*++result = tmp - value;

value = tmp;

}

return ++result;

}

template<class InputIterator,
class OutputIterator,
class BinaryOperation>

OutputIterator adjacent_difference(InputIterator first, InputIterator last,

OutputIterator result,

BinaryOperation binary_op)

{

if(first == last)
return result;

*result = *first;

return __adjacent_difference(first, last, result, value_type(first),

binary_op);

}

template<class InputIterator,
class OutputIterator,class T>

OutputIterator __adjacent_difference(InputIterator first, InputIterator last,

OutputIterator result, T*,

BinaryOperation binary_op)

{

T value = *first;

while(++first != last)

{

T tmp = *first;

*++result = binary_op(tmp,value);

value = tmp;

}

return ++result;

}

//inner_product

//把两个区间中的数做 “内积”
并都 “加到” init的副本中并最后返回这副本

template<class InputIterator1,
class InputIterator2,class T>

T inner_product(InputIterator1 first1, InputIterator last1,

InputIterator2 first2, T init)

{

for(; first1 != last1; ++first1,++first2)

init = init + (*first1 * *first2);

return init;

}

template<class InputIterator1,
class InputIterator2,class T,

class BinaryOperation1,
class BinaryOperation2>

T inner_product(InputIterator1 first1, InputIterator last1,

InputIterator2 first2, T init, BinaryOperation1 binary_op1,

BinaryOperation2 binary_op2)

{

for(; first1 != last1; ++first1,++first2)

init = binary_op1(init, binary_op2(*first1, *first2));

return init;

}

//partial_sum

//把区间中的数都
累“加”
起来。 每加一次就输出一次到
指定迭代器。

template<class InputIterator,
class OutputIterator>

OutputIterator partial_sum(InputIterator first, InputIterator last,

OutputIterator result)

{

if(first == last)
return result;

*result = *first;

return __partial_sum(first, last, result, value_type(first));

}

template<class InputIterator,
class OutputIterator,class T>

OutputIterator __partial_sum(InputIterator first, InputIterator last,

OutputIterator result, T*)

{

T value = *first;

while(++first != last)

{

value = value + *first;

*++result = value;

}

return ++result;

}

template<class InputIterator,
class OutputIterator,
class BinaryOperation>

OutputIterator partial_sum(InputIterator first, InputIterator last,

OutputIterator result, BinaryOperation binary_op)

{

if(first == last)
return result;

*result = *first;

return __partial_sum(first, last, result, value_type(first), binary_op);

}

template<class InputIterator,
class OutputIterator,class T>

OutputIterator __partial_sum(InputIterator first, InputIterator last,

OutputIterator result, T*,

BinaryOperation binary_op)

{

T value = *first;

while(++first != last)

{

value = binary_op(value, *first);

*++result = value;

}

return ++result;

}

//power

template<class T,
class Interger>

inline T power(T x, Interger n)

{

return power(x,n,multiplies<T>());

}

template<class T,
class Interger, class MonoidOperation>

T power(T x, Interger n, MonoidOperation op)

{

)

return identity_element(op);

else

{

//确定 x的m次
值， 为了不重复计算，看n是否能被 x的m次
整除，通过移位便可确定

) ==
)

{

n >>=
;

x = op(x, x);

}

//也是为了不重复计算，把x的n次拆分成2^m+2^(m-1)+2^(m-2)+...+1

//先算出1次，再算出2次，再算出4次。只要对应位置上有数，加进reslt就行，

//没有数则不加。

T result = x;

n >>=
;

)

{

x = op(x, x);

) !=
)

result = op(result, x);

n >>=
;

}

return result;

}

}

// itoa

//在一个区间中依次写入value value+1...

template<class ForwardIterator,
class T>

void itoa(ForwardIterator first, ForwardIterator last, T value)

{

while(first != last)

*first++ = value++;

}

//****************************数值算法*****************************

//****************************基本算法*****************************

//equal

template<class InputIterator1,
class InputIterator2>

inline bool equal(InputIterator1 first1, InputIterator1 last1,

InputIterator2 first2)

{

for(; first != last1; ++first1,++first2)

if(*first1 != *first2)

return false;

return true;

}

template<class InputIterator1,
class InputIterator2,

class BinaryPredicate>

inline bool equal(InputIterator1 first1, InputIterator1 last1,

InputIterator2 first2, BinaryPredicate binary_op)

{

for(; first != last1; ++first1,++first2)

if(!binary_op(*first1,*first2))

return false;

return true;

}

//fill

template<class ForwardIterator,
class T>

void fill(ForwardIterator first, ForwardIterator last,
const T& value)

{

for(; first != last; ++first)

*first = value;

}

//fill_n

//这里少了比较 first不需要和last比较来确定中止条件
所以只需要一个output迭代器

template<class OutputIterator,
class Size, class T>

OutputIterator fill_n(OutputIterator first, Size n,
const T& value)

{

; --n, ++first)

*first = value;

return first;

}

//iter_swap

template<class ForwardIterator1,
class ForwardIterator2>

inline void iter_swap(ForwardIterator1 a, ForwardIterator2 b)

{

__iter_swap(a, b, value_type(a));

}

template<class ForwardIterator1,
class ForwardIterator2,
class T>

inline void __iter_swap(ForwardIterator1 a, ForwardIterator2 b, T*)

{

T tmp = *a;

*a = *b;

*b = tmp;

}

//lexicographical_compare
按字典比较

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;

}

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;

}

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));

? result <
: len1 < len2;

}

//max两者比较返回大值

template<class T>

inline const T& max(const T& a,
const T& b)

{

return a < b ? 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;

}

//min两者比较返回小值

template<class T>

inline const T& min(const T& a,
const T& b)

{

return b < a ? b : a;

}

template<class T,
class Compare>

inline const T& min(const T& a,
const T& b, Compare comp)

{

return comp(b,a) ? b : a;

}

//mismatch
找到第一个不匹配点

template<class InputIterator1,
class InputIterator2>

pair<InputIterator1, InputIterator2> mismatch(

InputIterator1 first1,

InputIterator1 last1,

InputIterator2 first2)

{

while (first != last1 && *first1 == *first2)

{

++first1;

++first2;

}

return pair<InputIterator1, InputIterator2>(first1, first2);

}

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);

}

//swap

template<class T>

inline void swap(T& a, T& b)

{

T tmp = a;

a = b;

b = tmp;

}

//copy这个函数为了强化效率下了血本

//正常版本走这边

template<class InputIterator,
class OutputIterator>

inline OutputIterator copy(InputIterator first, InputIterator last,

OutputIterator result)

{

return __copy_dispatch<InputIterator,OutputIterator>()

(first, last, result);

}

//char* wchar_t*
走这边

inline char* copy(const
char* first, const
char* last, char* result)

{

memmove(result, first, last - first);

return result + (last - first);

}

inline
wchar_t* copy(const
wchar_t* first, const
wchar_t* last,

const wchar_t* result)

{

memmove(result, first,
sizeof(wchar_t) * (last - first));

return result + (last - first);

}

//准备一个仿函数，用来再次特化，用仿函数可以根据传入的InputIterator来特化

//正常版本走这边

template<class InputIterator,
char OutputIterator>

struct __copy_dispatch

{

OutputIterator
operator()(InputIterator first, InputIterator last,

OutputIterator result)

{

//传入一个迭代器标签，区分是否是随机迭代器

return __copy(first, last, result, iterator_category(first));

}

};

//指针走这边

template<class T>

struct __copy_dispatch<T*, T*>

{

T*
operator()(T* first, T* last, T* result)

{

//判断
是否
没有 assignment_operator重载操作

typedef typename __type_traits<T>::has_trivial_assignment_operator t;

return __copy_t(first, last, result, t());

}

};

//const指针走这边

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());

}

};

//input是基类，不管forward
还是bidi迭代器都走这边

template<class InputIterator,
class OutputIterator>

inline OutputIterator __copy(InputIterator first, InputIterator last,

OutputIterator result, input_iterator_tag)

{

for(; first != last; ++result, ++first)

*result = *first;

return result;

}

//随机迭代器走这边

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));

}

//直接算出区间大小，根据大小来循环
不需要判断迭代是否相等，可以有效提升速度

template<class RandomAccessIterator,
class OutputIterator,
class Distance>

inline OutputIterator

__copy_d(RandomAccessIterator first, RandomAccessIterator last,

OutputIterator result, Distance*)

{

; --n, ++result, ++first )

*result = *first;

return result;

}

//是
没有assignment_operator重载操作的话
就走这。直接复制内存

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);

}

//不是
没有assignment_operator重载操作(也就是有重载)
走这边，调用随机迭代器的copy方法

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*)
);

}