C++ Tutorial/STL Algorithms Sorting/partial sort

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The generic partial_sort algorithms with predicate

#include <vector>
#include <algorithm>
#include <iostream>
#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;
}
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

/* 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);
    // 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);
}
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

/* 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);
    // 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);
}
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

/* 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);
    // 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);
}
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
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