C++ Tutorial/STL Algorithms Sorting/partial sort

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The generic partial_sort algorithms with predicate

<source lang="cpp">#include <vector>

  1. include <algorithm>
  2. include <iostream>
  3. include <iterator>

using namespace std; class comp_last {

public:
 bool operator()(int x, int y) const
   // Compare x and y based on their last base-10 digits:
 {
   return x  10;
 }

}; int main() {

 const int N = 20;
 vector<int> vector0;
 for (int i = 0; i < N; ++i)
  vector0.push_back(i);
 vector<int> vector1 = vector0;
 ostream_iterator<int> out(cout, " ");
 cout << "Before sorting:\n";
 copy(vector1.begin(), vector1.end(), out);
 cout << endl;
 sort(vector1.begin(), vector1.end(), comp_last());

 cout << "After sorting by last digits with sort:\n";
 copy(vector1.begin(), vector1.end(), out);
 cout << endl << endl;
 vector1 = vector0;
 reverse(vector1.begin(), vector1.end());
 cout << "Before sorting:\n";
 copy(vector1.begin(), vector1.end(), out);
 cout << endl << endl;
 partial_sort(vector1.begin(), vector1.begin() + 5,vector1.end(), comp_last());
 cout << "After sorting with partial_sort to get 5 values with smallest last digits:\n";
 copy(vector1.begin(), vector1.end(), out);
 cout << endl << endl;
 return 0;

}</source>

Before sorting:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
After sorting by last digits with sort:
10 0 11 1 12 2 13 3 4 14 5 15 6 16 7 17 8 18 9 19
Before sorting:
19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
After sorting with partial_sort to get 5 values with smallest last digits:
10 0 11 1 12 19 18 17 16 15 9 8 7 6 5 4 14 13 3 2

Use partial_sort to sort all 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.
*/
  1. include <iostream>
  2. include <vector>
  3. include <deque>
  4. include <list>
  5. include <set>
  6. include <map>
  7. include <string>
  8. include <algorithm>
  9. include <iterator>
  10. include <functional>
  11. 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);
   // sort all elements
   partial_sort (coll.begin(),      // beginning of the range
                 coll.end(),        // end of sorted range
                 coll.end());       // end of full range
   PRINT_ELEMENTS(coll);

}</source>

3 4 5 6 7 2 3 4 5 6 1 2 3 4 5
1 2 2 3 3 3 4 4 4 5 5 5 6 6 7

Use partial_sort to sort until the first five elements are sorted

<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.
*/
  1. include <iostream>
  2. include <vector>
  3. include <deque>
  4. include <list>
  5. include <set>
  6. include <map>
  7. include <string>
  8. include <algorithm>
  9. include <iterator>
  10. include <functional>
  11. 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);
   // sort until the first five elements are sorted
   partial_sort (coll.begin(),      // beginning of the range
                 coll.begin()+5,    // end of sorted range
                 coll.end());       // end of full range
   PRINT_ELEMENTS(coll);

}</source>

3 4 5 6 7 2 3 4 5 6 1 2 3 4 5
1 2 2 3 3 7 6 5 5 6 4 4 3 4 5

Use partial_sort with custom function to sort inversely until the first five elements are sorted

<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.
*/
  1. include <iostream>
  2. include <vector>
  3. include <deque>
  4. include <list>
  5. include <set>
  6. include <map>
  7. include <string>
  8. include <algorithm>
  9. include <iterator>
  10. include <functional>
  11. 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);
   // sort inversely until the first five elements are sorted
   partial_sort (coll.begin(),      // beginning of the range
                 coll.begin()+5,    // end of sorted range
                 coll.end(),        // end of full range
                 greater<int>());   // sorting criterion
   PRINT_ELEMENTS(coll);

}</source>

3 4 5 6 7 2 3 4 5 6 1 2 3 4 5
7 6 6 5 5 2 3 3 4 4 1 2 3 4 5