C++/STL Algorithms Modifying sequence operations/stable partition

Use stable_partition algorithms: preserving relative order in each group

<source lang="cpp">

1. include <algorithm>
2. include <vector>
3. include <string>
4. include <iostream>
5. include <iterator>

using namespace std; bool above40(int n) { return (n > 4); } int main() {

 const int N = 7;
 int array0[N] = {5, 3, 1, 7, 6, 4, 2};
 int array1[N];
 copy(&array0[0], &array0[N], &array1[0]);
 ostream_iterator<int> out(cout, " ");
 cout << "Original sequence:                 ";
 copy(&array1[0], &array1[N], out); cout << endl;
 // Partition array1, putting numbers greater than 4
 // first, followed by those less than or equal to 4,
 // preserving relative order in each group:
 int* split = stable_partition(&array1[0], &array1[N], above40);
 cout << "Result of stable partitioning:     ";
 copy(&array1[0], split, out); cout << "| ";
 copy(split, &array1[N], out); cout << endl;
 return 0;

} /* Original sequence: 5 3 1 7 6 4 2 Result of stable partitioning: 5 7 6 | 3 1 4 2

*/        
 </source>

Use stable_partition and partition

<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() {

  vector<int> coll1;
  vector<int> coll2;
  INSERT_ELEMENTS(coll1,1,9);
  INSERT_ELEMENTS(coll2,1,9);
  PRINT_ELEMENTS(coll1,"coll1: ");
  PRINT_ELEMENTS(coll2,"coll2: ");
  cout << endl;
  // move all even elements to the front
  vector<int>::iterator pos1, pos2;
  pos1 = partition(coll1.begin(), coll1.end(),         // range
                   not1(bind2nd(modulus<int>(),2)));   // criterion
  pos2 = stable_partition(coll2.begin(), coll2.end(),       // range
                          not1(bind2nd(modulus<int>(),2))); // crit.
  // print collections and first odd element
  PRINT_ELEMENTS(coll1,"coll1: ");
  cout << "first odd element: " << *pos1 << endl;
  PRINT_ELEMENTS(coll2,"coll2: ");
  cout << "first odd element: " << *pos2 << endl;

} /* coll1: 1 2 3 4 5 6 7 8 9 coll2: 1 2 3 4 5 6 7 8 9 coll1: 8 2 6 4 5 3 7 1 9 first odd element: 5 coll2: 2 4 6 8 1 3 5 7 9 first odd element: 1

*/
       
 </source>