STL算法之集合
集合的所有操作，都需要保证两个集合都已排好序。
| 算法 | 功能 |
|---|---|
| includes | 判断一个集合是否是另一个集合的子集 |
| implace_merge | 将已经排序好两部分归并 |
| merge | 归并排序 |
| set_difference | 集合差集 |
| set_intersection | 集合交集 |
| set_union | 集合并集 |
1 includes
函数原型：
template <class InputIterator1,class InputIterator2>
bool includes (InputIterator1 first1,InputIterator1 last1,
InputIterator2 first2,InputIterator2 last2 );
template <class InputIterator1,class InputIterator2, class Compare>
bool includes (InputIterator1 first1,InputIterator1 last1,
InputIterator2 first2,InputIterator2 last2,
Compare comp );- 判断 集合2 是否属于 集合1。
- 功能类似于 find_end 和 search，但是find_end（或search）并不要求”范围”是已经排好序的，只要求元素之间的顺序是一样的。
函数等价于：
template<class _InIt1,
class _InIt2,
class _Pr> inline
bool _Includes(_InIt1 _First1, _InIt1 _Last1,
_InIt2 _First2, _InIt2 _Last2, _Pr _Pred)
{ // test if set [_First1, _Last1) in [_First2, _Last2), using _Pred
for (; _First1 != _Last1 && _First2 != _Last2; )
if (_DEBUG_LT_PRED(_Pred, *_First2, *_First1))
return (false);
else if (_Pred(*_First1, *_First2))
++_First1;
else
{ // advance both
++_First1;
++_First2;
}
return (_First2 == _Last2);
}示例1：
#include <iostream> // std::cout
#include <algorithm> // std::includes, std::sort
bool myfunction (int i, int j) { return i<j; }
int main () {
int container[] = {5,10,15,20,25,30,35,40,45,50};
int continent[] = {40,30,20,10};
std::sort (container,container+10);
std::sort (continent,continent+4);
if ( std::includes(container,container+10,continent,continent+4) )
std::cout << "container includes continent!\n";
// using myfunction as comp:
if ( std::includes(container,container+10,continent,continent+4, myfunction) )
std::cout << "container includes continent!\n";
return 0;
}2 inplace_merge
函数原型：
template <class BidirectionalIterator>
void inplace_merge (BidirectionalIterator first, BidirectionalIterator middle,
BidirectionalIterator last);
template <class BidirectionalIterator, class Compare>
void inplace_merge (BidirectionalIterator first, BidirectionalIterator middle,
BidirectionalIterator last, Compare comp);示例2：
#include <iostream> // std::cout
#include <algorithm> // std::inplace_merge, std::sort, std::copy
#include <vector> // std::vector
int main () {
int first[] = {5,10,15,20,25};
int second[] = {50,40,30,20,10};
std::vector<int> v(10);
std::vector<int>::iterator it;
std::sort (first,first+5);
std::sort (second,second+5);
it=std::copy (first, first+5, v.begin());
std::copy (second,second+5,it);
std::inplace_merge (v.begin(),v.begin()+5,v.end());
std::cout << "The resulting vector contains:";
for (it=v.begin(); it!=v.end(); ++it)
std::cout << ' ' << *it;
std::cout << '\n';
return 0;
}3 merge
函数原型：
template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator merge (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result);
template <class InputIterator1, class InputIterator2,
class OutputIterator, class Compare> OutputIterator merge (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp);- 归并排序：将范围1 和 范围2 归并到 result，要求范围1和2都已经排序好。
函数等价于:
template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator merge (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result)
{
while (true) {
if (first1==last1) return std::copy(first2,last2,result);
if (first2==last2) return std::copy(first1,last1,result);
*result++ = (*first2<*first1)? *first2++ : *first1++; } }示例3：
#include <iostream> // std::cout
#include <algorithm> // std::merge, std::sort
#include <vector> // std::vector
int main () {
int first[] = {5,10,15,20,25};
int second[] = {50,40,30,20,10};
std::vector<int> v(10);
std::sort (first,first+5);
std::sort (second,second+5);
std::merge (first,first+5,second,second+5,v.begin());
std::cout << "The resulting vector contains:";
for (std::vector<int>::iterator it=v.begin(); it!=v.end(); ++it)
std::cout << ' ' << *it;
std::cout << '\n';
return 0;
}4 set_difference
函数原型：
template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_difference (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result);
template <class InputIterator1, class InputIterator2,
class OutputIterator, class Compare> OutputIterator set_difference (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp);- 获得两个集合的差集。两个输入序列须保证已排好序。F1-F2，即F1有的，F2没有的。
函数等价于：
template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_difference (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result)
{
while (first1!=last1 && first2!=last2)
{
if (*first1<*first2) { *result = *first1; ++result; ++first1; }
else if (*first2<*first1) ++first2;
else { ++first1; ++first2; }
}
return std::copy(first1,last1,result);
}示例4：
#include <iostream> // std::cout
#include <algorithm> // std::set_difference, std::sort
#include <vector> // std::vector
int main () {
int first[] = {5,10,15,20,25};
int second[] = {50,40,30,20,10};
std::vector<int> v(10); // 0 0 0 0 0 0 0 0 0 0
std::vector<int>::iterator it;
std::sort (first,first+5); // 5 10 15 20 25
std::sort (second,second+5); // 10 20 30 40 50
it=std::set_difference (first, first+5, second, second+5, v.begin());
// 5 15 25 0 0 0 0 0 0 0
v.resize(it-v.begin()); // 5 15 25
std::cout << "The difference has " << (v.size()) << " elements:\n";
for (it=v.begin(); it!=v.end(); ++it)
std::cout << ' ' << *it;
std::cout << '\n';
return 0;
}5 set_intersection
函数原型：
template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_intersection (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result);
template <class InputIterator1, class InputIterator2,
class OutputIterator, class Compare> OutputIterator set_intersection (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp);- 集合的交集。集合要求已经排好序。
函数等价于：
template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_intersection (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result)
{
while (first1!=last1 && first2!=last2)
{
if (*first1<*first2) ++first1;
else if (*first2<*first1) ++first2;
else {
*result = *first1;
++result; ++first1; ++first2;
}
}
return result;
}示例5：
#include <iostream> // std::cout
#include <algorithm> // std::set_intersection, std::sort
#include <vector> // std::vector
int main () {
int first[] = {5,10,15,20,25};
int second[] = {50,40,30,20,10};
std::vector<int> v(10); // 0 0 0 0 0 0 0 0 0 0
std::vector<int>::iterator it;
std::sort (first,first+5); // 5 10 15 20 25
std::sort (second,second+5); // 10 20 30 40 50
it=std::set_intersection (first, first+5, second, second+5, v.begin());
// 10 20 0 0 0 0 0 0 0 0
v.resize(it-v.begin()); // 10 20
std::cout << "The intersection has " << (v.size()) << " elements:\n";
for (it=v.begin(); it!=v.end(); ++it)
std::cout << ' ' << *it;
std::cout << '\n';
return 0;
}6 set_union
函数原型：
template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_union (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result);
custom (2)
template <class InputIterator1, class InputIterator2,
class OutputIterator, class Compare> OutputIterator set_union (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp);- 集合并集。要求集合已经排序。
函数等价于：
template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_union (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result)
{
while (true)
{
if (first1==last1) return std::copy(first2,last2,result);
if (first2==last2) return std::copy(first1,last1,result);
if (*first1<*first2) { *result = *first1; ++first1; }
else if (*first2<*first1) { *result = *first2; ++first2; }
else { *result = *first1; ++first1; ++first2; }
++result;
}
}示例6：
#include <iostream> // std::cout
#include <algorithm> // std::set_union, std::sort
#include <vector> // std::vector
int main () {
int first[] = {5,10,15,20,25};
int second[] = {50,40,30,20,10};
std::vector<int> v(10); // 0 0 0 0 0 0 0 0 0 0
std::vector<int>::iterator it;
std::sort (first,first+5); // 5 10 15 20 25
std::sort (second,second+5); // 10 20 30 40 50
it=std::set_union (first, first+5, second, second+5, v.begin());
// 5 10 15 20 25 30 40 50 0 0
v.resize(it-v.begin()); // 5 10 15 20 25 30 40 50
std::cout << "The union has " << (v.size()) << " elements:\n";
for (it=v.begin(); it!=v.end(); ++it)
std::cout << ' ' << *it;
std::cout << '\n';
return 0;
}