//---------------------------15/03/31----------------------------
//lower_bound(要求有序)
template<class ForwardIterator, class T>
inline ForwardIterator lower_bound(ForwardIterator first,
ForwardIterator last,
const T& value)
{
return __lower_bound(first, last, value, distance_type(first),
iterator_category(first));
}
//采用二分法来寻找第一个允许插入的位置
template<class ForwardIterator, class T, class Distance>
ForwardIterator __lower_bound(ForwardIterator first,
ForwardIterator last,
const T& value, Distance*
forward_iterator_tag)
{
Distance len = 0;
//取到数组大小len
distance(first, last, len);
Distance half;
ForwardIterator middle;
while (len > 0)
{
//找到中间的位置，取”下界“，然而其实是取half＋1，因为这里是first+half
//虽然取的是下界 比如len=3 取到half＝1， first+1 就是第2个
half = len >> 1;
middle = first;
advance(middle, half);
if(*middle < value)
{
first = middle;
++first;
//first一开始指向 half＋1的元素，所以右边剩下的是 len－half－1
len = len - half - 1;
}
else
len = half;
}
return first;
}
//其实感觉没有必要使用两个版本，distance函数和advance函数底层就已经对迭代器进行分类运算了
//效率上应该不会差的。
template<class RandomAccessIterator, class T, class Distance>
RandomAccessIterator __lower_bound(RandomAccessIterator first,
RandomAccessIterator last,
const T& value, Distance*,
random_access_iterator_tag)
{
Distance len = last - first;
Distance half;
RandomAccessIterator middle;
while (len > 0)
{
half = len >> 1;
middle = first + half;
if(*middle < value)
{
first = middle + 1;
len = len - half - 1;
}
else
len = half;
}
return first;
}
//upper_bound(要求有序)
template<class ForwardIterator, class T>
inline ForwardIterator upper_bound(ForwardIterator first,
ForwardIterator last,
const T& value)
{
return __upper_bound(first, last, value, distance_type(first),
iterator_category(first));
}
template<class ForwardIterator, class T, class Distance>
ForwardIterator __upper_bound(ForwardIterator first,
ForwardIterator last,
const T& value, Distance*
forward_iterator_tag)
{
Distance len = 0;
//取到数组大小len
distance(first, last, len);
Distance half;
ForwardIterator middle;
while (len > 0)
{
//和lower_bound不一样，当 value 等于 middle 时是向右走的。所以指向
//的位置的值不是value，而是第一个大于value的值
half = len >> 1;
middle = first;
advance(middle, half);
if(value < *middle)
len = half;
else
{
first = middle;
++first;
len = len - half - 1;
}
}
return first;
}
template<class RandomAccessIterator, class T, class Distance>
RandomAccessIterator __upper_bound(RandomAccessIterator first,
RandomAccessIterator last,
const T& value, Distance*,
random_access_iterator_tag)
{
Distance len = last - first;
Distance half;
RandomAccessIterator middle;
while (len > 0)
{
half = len >> 1;
middle = first + half;
if(value < *middle)
len = half;
else
{
first = middle+1;
len = len -half -1;
}
}
return first;
}
//binary_search(要求有序)
template<class ForwardIterator, class T>
bool binary_search(ForwardIterator first, ForwardIterator last,
const T& value)
{
ForwardIterator i =lower_bound(first, last, value);
return i != last && !(value < *i);
//如果不存在，使用lower_bound获得的*i > value;所以如果value < *i说明没找到
}
template<class ForwardIterator, class T, class Compare>
bool binary_search(ForwardIterator first, ForwardIterator last,
const T& value, Compare comp)
{
ForwardIterator i = lower_bound(first, last, value, comp);
return i != last && !comp(value, *i);
}
//next_permutation
/*
下一个排列组合：
abc，acb，bac，bca，cab，cba。依次排序，前面的元素最迟改变，
把后面的都排序一遍，当前面的元素改变时，最后的元素要依次排序
acbd的 b<d，所以固定前面元素，得到acdb，再下一个 d>b c < d所以可以让c 变成d 得到adbc
*/
template<class BidirectionalIterator>
bool next_permutation(BidirectionalIterator first,
BidirectionalIterator last)
{
if(first == last)
return false;
BidirectionalIterator i = first;
++i;
if(i == last)
return false;
//区间没有元素和只有一个元素都返回false；
i = last;
-- i;
//i＝最后一个元素
for(;;)
{
//ii成了最后一个元素
BidirectionalIterator ii = i;
//i成了最后一个元素的前驱
--i;
//只要不是成倒序的就可以找到 *i < *ii，如果是倒序的说明没有下一个排列组合了
if(*i < *ii)
{
/*
现在情况是 i d c... j 首先 d > c >... > j
i < d 。因为后面都是倒序的，我们要找到一个比i大一阶的数填到i的位置。
所以while(!(*i < *--j)只要j小于等于i就左走，找到一个大于i的就可以把
这个数放入i的位置，把i放入j的位置。i放到j的位置。d开始到末尾的序列还是倒序的
所以要reverse( d c ... last)d就是ii在的位置
*/
BidirectionalIterator j =last;
while(!(*i < *--j));
iter_swap(i, j);
reverse(ii, last);
return true;
}
if(i == first)
{
//整个序列时倒序的，直接把它变成正序就好了。并要返回false
reverse(first, last);
return false;
}
}
}
//prev_permutation
template<class BidirectionalIterator>
bool prev_permutation(BidirectionalIterator first,
BidirectionalIterator last)
{
if(first == last)
return false;
BidirectionalIterator i = first;
++i;
if(i == last)
return false;
i = last;
--i;
//和next操作刚好相反，先找到一个数比他后驱大，再找到比他小一阶的数交换，之后反转
for(;;)
{
BidirectionalIterator ii = i;
--i;
if(*ii < *i)
{
BidirectionalIterator j =last;
while(!(*--j < *i));
iter_swap(i, j);
reverse(ii, last);
return true;
}
if(i == first)
{
reverse(first, last);
return false;
}
}
}
//random_shuffle
//对区间[first,last)随机产生一个排列
template<class RandomAccessIterator>
inline void random_shuffle(RandomAccessIterator first,
RandomAccessIterator last)
{
__random_shuffle(first, last, distance_type(first));
}
template<class RandomAccessIterator, class Distance>
void __random_shuffle(RandomAccessIterator first,
RandomAccessIterator last,
Distance*)
{
if(first == last)
return;
for(RandomAccessIterator i =first + 1; i != last; ++i)
#ifdef __STL_NO_DRAND48
iter_swap(i, first + Distance(rand()%((i - first) + 1)));
#else
iter_swap(i, first + Distance(lrand48() % ((i - first) + 1)));
#endif
}
template<class RandomAccessIterator, class RandomNumberGenerator>
void random_shuffle(RandomAccessIterator first, RandomAccessIterator last,
RandomNumberGenerator& rand)
{
if(first == last)
return;
for(RandomAccessIterator i = first + 1; i != last; ++i)
iter_swap(i, first + rand((i - first) + 1));
}
//partial_sort
//基于堆来对前面部分数据进行排序
template<class RandomAccessIterator>
inline void partial_sort(RandomAccessIterator first,
RandomAccessIterator middle,
RandomAccessIterator last)
{
__partial_sort(first, middle, last, value_type(first));
}
template<class RandomAccessIterator, class T>
void __partial_sort(RandomAccessIterator first,
RandomAccessIterator middle,
RandomAccessIterator last,T*)
{
make_heap(first, middle);
for(RandomAccessIterator i = middle; i < last; ++i)
{
if(*i < *first)
__pop_heap(first, middle, i, T(*i), distance_type(first));
sort_heap(first, middle);
}
}
//sort
//Insetion Sort
template<class RandomAccessIterator>
void __insertion_sort(RandomAccessIterator first,
RandomAccessIterator last)
{
if(first == last)
return ;
for(RandomAccessIterator i =first + 1; i != last; ++i)
__linear_insert(first, i,value_type(first));
}
template<class RandomAccessIterator, class T>
inline void __linear_insert(RandomAccessIterator first,
RandomAccessIterator last, T*)
{
T value = *last;
//确保第一个元素是最小的
if(value < *first)
{
copy_backward(first, last, last + 1);
*first = value;
}
else
__unguarded_linear_insert(last, value);
}
template<class RandomAccessIterator, class T>
void __unguarded_linear_insert(RandomAccessIterator last, T value)
{
//插入排序，从尾部开始比较，原因是这样正好可以边比较边把元素后移，
//不需要找到位置然后都后移一次。
RandomAccessIterator next = last;
--next;
//不用判断越界，前面已经保证头部是最小的了
while (value < *next)
{
*last = *next;
last = next;
--next;
}
*last = value;
}
//取中间值
template<class T>
inline const T& __median(const T& a, const T& b, const T& c)
{
if(a < b)
if(b < c)
return b; //a < b < c
else if(a < c)
return c; //a < b, b >= c, a<c
else
return a;
else if(a < c) //c > a >=b
return a;
else if(b < c) // a >=b, a <= c, b < c
return c;
else
return b;
}
//很正常的快排划分步骤最后得到的结果是 first后面包括first的值是大于等于pivot值的
//first前面的值是小于pivot值的
template<class RandomAccessIterator, class T>
RandomAccessIterator __unguarded_partition(RandomAccessIterator first,
RandomAccessIterator last,
T pivot)
{
while (true)
{
while (*first < pivot)
++first;
--last;
while(pivot < *last)
--last;
if(!(first < last))
return first;
iter_swap(first, last);
++first;
}
}
//真正的sort
template<class RandomAccessIterator>
inline void sort(RandomAccessIterator first,
RandomAccessIterator last)
{
if(first != last)
{
__introsort_loop(first, last, value_type(first), __lg(last - first)*2);
__final_insertion_sort(first, last);
}
}
template<class Size>
inline Size __lg(Size n)
{
Size k;
for(k = 0; n > 1; n >>= 1)
++k;
return k;
}
template<class RandomAccessIterator, class T, class Size>
void __introsort_loop(RandomAccessIterator first,
RandomAccessIterator last, T*,
Size depth_limit)
{
//__stl_treshold 是全局常数 为const int 16
while (last - first > __stl_threshold)
{
if (depth_limit == 0)
{
//如果调用深度到达限制就改调用堆排序
partial_sort(first, last, last);
return;
}
//深度减一
--depth_limit;
//调用一次划分返回 关键元素的迭代器
RandomAccessIterator cur = __unguarded_partition(
first, last, T(__median(*first,
*(first + (last - first) / 2),
*(last - 1))));
//对右边进行迭代
__introsort_loop(cur, last, value_type(first), depth_limit);
last = cur;
}
}
template<class RandomAccessIterator>
void __final_insertion_sort(RandomAccessIterator first,
RandomAccessIterator last)
{
if (last - first > __stl_threshold)
{
__insertion_sort(first, first + __stl_threshold);
__unguarded_insertion_sort(first + __stl_threshold, last);
}
else
__insertion_sort(first, last);
}
template<class RandomAccessIterator>
inline void __unguarded_insertion_sort(RandomAccessIterator first,
RandomAccessIterator last)
{
__unguarded_insertion_sort_aux(first, last, value_type(first));
}
template<class RandomAccessIterator, class T>
void __unguarded_insertion_sort_aux(RandomAccessIterator first,
RandomAccessIterator last,
T*)
{
for(RandomAccessIterator i = first; i != last; ++i)
__unguarded_linear_insert(i, T(*i));
}
/*
sort总结：先采用快排，有两种情况产生：
1>深度没有超出极限，会诞生一个个区间，每个区间大小 小于等于__stl_threshold(默认为16)，
然后对前16个采用插入排序，需要判断尾元素是否小于first元素。这次调用完就确保first是最小的
然后再调用__unguarded_linear_sort就可以少一个判断，也就可以从first + __stl_threshold
的地方进行开始调用__unguared_linear_sort，插入位置会一直往左，有可能会越过first + __stl_threshold
的位置。
(ps:一开始我想不明白的一点是，如果先对前16个元素调用一次__unguarded_linear_insert，那如果当初划分时
前面13个(只要小于16就行)是一个区间，那不是会把后面的3个元素牵扯进来，如果后面的3个元素不是最小的三个
那排序不就失败了，我当时想的是final sort那调用__unguarded_linear_insert(first +__stl_threshold, last)
会以first +__stl_threshold为first区间，对之后的所有元素进行排序，会造成一个问题，前16个中有比后面
大的元素。后来才发现sgi的奇妙设计，那个while (value < *next),并没有越界判断，所以会一直往左搜索。)
2>迭代深度超出限制，会对之后迭代的区间进行堆排序，这时剩下的区间就是不确定的，有已经排序好的(深度超出限制)，
也有没排序的(快排迭代达到16个元素的)，再次调用插入排序，对所有区间整理一遍。
*/
//equal_range(要求有序)
//返回由 等于传入值 的元素 组成的区间
template<class ForwardIterator, class T>
inline pair<ForwardIterator, ForwardIterator>
equal_range(ForwardIterator first, ForwardIterator last,
const T& value)
{
return __equal_range(first, last, value, distance_type(first),
iterator_category(first));
}
template<class RandomAccessIterator, class T, class Distance>
pair<RandomAccessIterator, RandomAccessIterator>
__equal_range(RandomAccessIterator first, RandomAccessIterator last,
const T& value, Distance*, random_access_iterator_tag)
{
Distance len = last - first;
Distance half;
RandomAccessIterator middle, left, right;
while (len > 0)
{
half = len >> 1;
middle = first + half;
if(*middle < value)
{
first = middle + 1;
len = len - half -1;
}
else if(value < *middle)
len = half;
else
{
left = lower_bound(first, middle, value);
right = upper_bound(++middle, first + len, value);
return pair<RandomAccessIterator, RandomAccessIterator>(left, right);
}
//因为lower_bound和upper_bound都会调用同样的步骤直到相等。
}
return pair<RandomAccessIterator, RandomAccessIterator>(first, first);
//在没有value值的情况下，返回一个区间[first,first)也就是first＝last的情况，这样可以表示
//没有相应元素。
}
template<class ForwardIterator, class T, class Distance>
pair<ForwardIterator, ForwardIterator>
__equal_range(ForwardIterator first, ForwardIterator last,
const T& value, Distance*, forward_iterator_tag)
{
Distance len = last - first;
Distance half;
ForwardIterator middle, left, right;
while (len > 0)
{
half = len >> 1;
middle = first;
advance(middle, half);
if(*middle < value)
{
first = middle;
++first;
len = len - half -1;
}
else if(value < *middle)
len = half;
else
{
left = lower_bound(first, middle, value);
advance(first, len);
right = upper_bound(++middle, first, value);
return pair<ForwardIterator, ForwardIterator>(left, right);
}
}
return pair<ForwardIterator, ForwardIterator>(first, first);
}
原文地址：http://blog.csdn.net/boydfd/article/details/44789001
