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==Finding the Median==

<source lang="cpp">
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
template <class T>
void print(T& c){
for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
std::cout << *i << endl;
}
}
int main( ) {
const int len = 9;
const int a[len] = { 5, 6, 4, 3,2, 6, 7, 9, 3 };
vector<int> v( a, a+len );
print( v );
// midpoint is the median
nth_element( v.begin(), v.begin()+len/2,v.end() );
print( v );
cout << "\nMedian salary: " << v[len/2];
// display sorted v for clarity
sort( v.begin(), v.end() );
print( v );
}

</source>

==Illustrating the generic nth_element algorithm==

<source lang="cpp">

#include <iostream>
#include <cassert>
#include <algorithm>
#include <vector>
using namespace std;
int main()
{
vector<int> v(7);
v[0] = 25;
v[1] = 7;
v[2] = 9;
v[3] = 2;
v[4] = 0;
v[5] = 5;
v[6] = 21;
const int N = 4;
// Use nth_element to place the Nth smallest
// element in v in the Nth position, v.begin() + N:
nth_element(v.begin(), v.begin() + N, v.end());

for (int i = 0; i < N; ++i)
assert (v[N] >= v[i]);

for (int i = N + 1; i < 7; ++i)
cout << v[N];
return 0;
}
/*
99
*/

</source>

==Use nth_element to extract the four highest elements==

<source lang="cpp">

/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
deque<int> coll;
INSERT_ELEMENTS(coll,3,7);
INSERT_ELEMENTS(coll,2,6);
INSERT_ELEMENTS(coll,1,5);
PRINT_ELEMENTS(coll);
// extract the four highest elements
nth_element (coll.begin(), // beginning of range
coll.end()-4, // element that should be sorted correctly
coll.end()); // end of range
// print them
cout << "the four highest elements are: ";
copy (coll.end()-4, coll.end(),
ostream_iterator<int>(cout," "));
cout << endl;
}
/*
3 4 5 6 7 2 3 4 5 6 1 2 3 4 5
the four highest elements are: 5 6 7 6
*/

</source>

==Use nth_element to extract the four lowest elements==

<source lang="cpp">

/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
deque<int> coll;
INSERT_ELEMENTS(coll,3,7);
INSERT_ELEMENTS(coll,2,6);
INSERT_ELEMENTS(coll,1,5);
PRINT_ELEMENTS(coll);
// extract the four lowest elements
nth_element (coll.begin(), // beginning of range
coll.begin()+3, // element that should be sorted correctly
coll.end()); // end of range
// print them
cout << "the four lowest elements are: ";
copy (coll.begin(), coll.begin()+4,
ostream_iterator<int>(cout," "));
cout << endl;
}
/*
3 4 5 6 7 2 3 4 5 6 1 2 3 4 5
the four lowest elements are: 2 1 2 3
*/

</source>

==Use nth_element with custom function to extract the four highest elements==

<source lang="cpp">

/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}
using namespace std;
int main()
{
deque<int> coll;
INSERT_ELEMENTS(coll,3,7);
INSERT_ELEMENTS(coll,2,6);
INSERT_ELEMENTS(coll,1,5);
PRINT_ELEMENTS(coll);
// extract the four highest elements (second version)
nth_element (coll.begin(), // beginning of range
coll.begin()+3, // element that should be sorted correctly
coll.end(), // end of range
greater<int>()); // sorting criterion
// print them
cout << "the four highest elements are: ";
copy (coll.begin(), coll.begin()+4,
ostream_iterator<int>(cout," "));
cout << endl;
}
/*
3 4 5 6 7 2 3 4 5 6 1 2 3 4 5
the four highest elements are: 6 7 6 5
*/

</source>

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в 14:21, 25 мая 2010

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