不会改变操作对象内容的STL算法(元素查找，序列查找，统计元素个数，比较区间，找最值)

元素查找，序列查找，统计元素个数，比较区间，找最值

一、单个元素查找: find, find_if, adjacent_find, find_first_of

1、find：查找元素val

template<class InputIterator, class T>
InputIterator find (InputIterator first, InputIterator last, const T& val)
{
while (first!=last) {
if (*first==val) return first;
++first;
}
return last;
}

2、find_if：查找满足pred(*first)条件的元素

template<class InputIterator, class UnaryPredicate>
InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred)
{
while (first!=last) {
if (pred(*first)) return first;
++first;
}
return last;
}

此时可能的UnaryPredicate有，bind2nd(equal_to<int>(), 0)，bind2nd(less<int>(), 0),自定义等

3、adjacent_find：查找两个相邻的元素或者前后两个元素满足条件pred(*first,*next)

template <class ForwardIterator>
ForwardIterator adjacent_find (ForwardIterator first, ForwardIterator last)
{
if (first != last)
{
ForwardIterator next=first; ++next;
while (next != last) {
if (*first == *next)     // or: if (pred(*first,*next)), for version (2)
return first;
++first; ++next;
}
}
return last;
}

4、find_first_of:查找[first1,last1)内第一个等于[first2,last2)内的任意一个元素，或满足条件pred(*it,*first)的元素

template<class InputIterator, class ForwardIterator>
InputIterator find_first_of ( InputIterator first1, InputIterator last1,
ForwardIterator first2, ForwardIterator last2)
{
while (first1!=last1) {
for (ForwardIterator it=first2; it!=last2; ++it) {
if (*it==*first1)          // or: if (pred(*it,*first)) for version (2)
return first1;
}
++first1;
}
return last1;
}

二、子序列匹配（子序列查找）: search, find_end, search_n

1、search 在区间[first1,last1)查找第一次出现的子序列[first2,last2)

Searches the range [first1,last1) for the first occurrence of the sequence defined by [first2,last2), and returns an iterator to its first element, or last1 if no occurrences are found.

template<class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 search ( ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2)
{
if (first2==last2) return first1;  // specified in C++11

while (first1!=last1)
{
ForwardIterator1 it1 = first1;
ForwardIterator2 it2 = first2;
while (*it1==*it2) {    // or: while (pred(*it1,*it2)) for version 2
++it1; ++it2;
if (it2==last2) return first1;
if (it1==last1) return last1;
}
++first1;
}
return last1;
}

2、find_end 在区间[first1,last1)查找最后一次出现的子序列[first2,last2)

这个函数名字有点问题，不应该和find归在一起，应该是search_end

Searches the range [first1,last1) for the last occurrence of the sequence defined by [first2,last2), and returns an iterator to its first element, or last1 if no occurrences are found.

template<class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2)
{
if (first2==last2) return last1;  // specified in C++11

ForwardIterator1 ret = last1;

while (first1!=last1)
{
ForwardIterator1 it1 = first1;
ForwardIterator2 it2 = first2;
while (*it1==*it2) {    // or: while (pred(*it1,*it2)) for version (2)
++it1; ++it2;
if (it2==last2) { ret=first1; break; }
if (it1==last1) return ret;
}
++first1;
}
return ret;
}

3、search_n 查找区间[first,last)中由count个相邻元素形成的子序列，其中所有元素都等于value

Searches the range [first,last) for a sequence of count elements, each comparing equal to val (or for which pred returns true).

template<class ForwardIterator, class Size, class T>
ForwardIterator search_n (ForwardIterator first, ForwardIterator last,
Size count, const T& val)
{
ForwardIterator it, limit;
Size i;

limit=first; std::advance(limit,std::distance(first,last)-count);

while (first!=limit)
{
it = first; i=0;
while (*it==val)       // or: while (pred(*it,val)) for the pred version
{ ++it; if (++i==count) return first; }
++first;
}
return last;
}

三、计算区间中某个元素个数:count, count_if

1、count：计算区间[first,last)中和val相等的元素的个数

template <class InputIterator, class T>
typename iterator_traits<InputIterator>::difference_type
count (InputIterator first, InputIterator last, const T& val)
{
typename iterator_traits<InputIterator>::difference_type ret = 0;
while (first!=last) {
if (*first == val) ++ret;
++first;
}
return ret;
}

2、count_if:计算区间[first,last)中满足条件pred(*first)的元素的个数

template <class InputIterator, class UnaryPredicate>
typename iterator_traits<InputIterator>::difference_type
count (InputIterator first, InputIterator last, UnaryPredicate pred)
{
typename iterator_traits<InputIterator>::difference_type ret = 0;
while (first!=last) {
if (pred(*first)) ++ret;
++first;
}
return ret;
}

此时可能的UnaryPredicate有，bind2nd(equal_to<int>(), 0)，bind2nd(less<int>(), 0),自定义等

四、for_each遍历区间[first,last)中的每个元素并将Function fn套用在每个元素上

template<class InputIterator, class Function>
Function for_each(InputIterator first, InputIterator last, Function fn)
{
while (first!=last) {
fn (*first);
++first;
}
return fn;      // or, since C++11: return move(fn);
}

五：比较两个区间:equal, mismatch, lexicographical_compare

1、equal：当区间[first1,last1)中的元素和区间[first2,first2+（last1-first1))一一比较，如果都相等或满足pred(*first1,*first2)条件，则返回true，否则返回false

template <class InputIterator1, class InputIterator2>
bool equal ( InputIterator1 first1, InputIterator1 last1, InputIterator2 first2 )
{
while (first1!=last1) {
if (!(*first1 == *first2))   // or: if (!pred(*first1,*first2)), for version 2
return false;
++first1; ++first2;
}
return true;
}

2、mismatch：返回区间[first1,last1)中的元素和区间[first2,first2+（last1-first1))之间第一个元素值不同的位置(有两个位置，每个区间一个)

template <class InputIterator1, class InputIterator2>
pair<InputIterator1, InputIterator2>
mismatch (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2 )
{
while ( (first1!=last1) && (*first1==*first2) )  // or: pred(*first1,*first2), for version 2
{ ++first1; ++first2; }
return std::make_pair(first1,first2);
}

3、lexicographical_compare：以字典排序法比较，[first1,last1)小于[first2,last2)的话，返回true，否则返回false

template <class InputIterator1, class InputIterator2>
bool lexicographical_compare (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2);

template <class InputIterator1, class InputIterator2, class Compare>
bool lexicographical_compare (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
Compare comp);

template <class InputIterator1, class InputIterator2>
bool lexicographical_compare (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2)
{
while (first1!=last1)
{
if (first2==last2 || *first2<*first1) return false;
else if (*first1<*first2) return true;
++first1; ++first2;
}
return (first2!=last2);
}

六：最大值和最小值：min, max, min_element, max_element

1、min:返回两个对象a, b之间比较小的那个或满足!comp(b,a)?a:b;

template <class T> const T& min (const T& a, const T& b) {
return !(b<a)?a:b;     // or: return !comp(b,a)?a:b; for version (2)
}

2、max：返回两个对象a, b之间比较大的那个或满足!comp(b,a)?a:b;

template <class T> const T& max (const T& a, const T& b) {
return (a<b)?b:a;     // or: return comp(a,b)?b:a; for version (2)
}

3、min_element:找到区间[first,last)内最小的元素

template <class ForwardIterator>
ForwardIterator min_element ( ForwardIterator first, ForwardIterator last )
{
if (first==last) return last;
ForwardIterator smallest = first;

while (++first!=last)
if (*first<*smallest)    // or: if (comp(*first,*smallest)) for version (2)
smallest=first;
return smallest;
}

4、max_element:找到区间[first,last)内最大的元素

template <class ForwardIterator>
ForwardIterator max_element ( ForwardIterator first, ForwardIterator last )
{
if (first==last) return last;
ForwardIterator largest = first;

while (++first!=last)
if (*largest<*first)    // or: if (comp(*largest,*first)) for version (2)
largest=first;
return largest;
}