inplace_merge

     Algorithm

Merge two sorted sequences into one.

Contents

• Synopsis
• Description
• Complexity
• Example
• Warnings
• See Also

#include <algorithm>

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);

The inplace_merge algorithm merges two sorted consecutive ranges [first, middle) and [middle, last), and puts the result of the merge into the range [first, last). The merge is stable, that is, if the two ranges contain equivalent elements, the elements from the first range always precede the elements from the second.

There are two versions of the inplace_merge algorithm. The first version uses the less than operator (operator<) as the default for comparison, and the second version accepts a third argument that specifies a comparison operator.

When enough additional memory is available, inplace_merge does at most (last - first) - 1 comparisons. If no additional memory is available, an algorithm with O(NlogN) complexity (where N is equal to last-first) may be used.

//
// merge.cpp
//
 #include <algorithm>
 #include <vector>
 #include <iostream.h>
 int main()
 {
   int d1[4] = {1,2,3,4};
   int d2[8] = {11,13,15,17,12,14,16,18};
   // Set up two vectors
   vector<int> v1(d1,d1 + 4), v2(d1,d1 + 4);
   // Set up four destination vectors
   vector<int> v3(d2,d2 + 8),v4(d2,d2 + 8),
               v5(d2,d2 + 8),v6(d2,d2 + 8);
   // Set up one empty vector
   vector<int> v7;

   // Merge v1 with v2
   merge(v1.begin(),v1.end(),v2.begin(),v2.end(),v3.begin());
   // Now use comparator
   merge(v1.begin(),v1.end(),v2.begin(),v2.end(),v4.begin(),
         less<int>());

   // In place merge v5
   vector<int>::iterator mid = v5.begin();
   advance(mid,4);
   inplace_merge(v5.begin(),mid,v5.end());
   // Now use a comparator on v6
   mid = v6.begin();
   advance(mid,4);
   inplace_merge(v6.begin(),mid,v6.end(),less<int>()); 

   // Merge v1 and v2 to empty vector using insert iterator

   merge(v1.begin(),v1.end(),v2.begin(),v2.end(),
         back_inserter(v7));

   // Copy all cout
   ostream_iterator<int> out(cout," ");
   copy(v1.begin(),v1.end(),out);
   cout << endl;
   copy(v2.begin(),v2.end(),out);
   cout << endl;
   copy(v3.begin(),v3.end(),out);
   cout << endl;
   copy(v4.begin(),v4.end(),out);
   cout << endl;
   copy(v5.begin(),v5.end(),out);
   cout << endl;
   copy(v6.begin(),v6.end(),out);
   cout << endl;
   copy(v7.begin(),v7.end(),out);
   cout << endl;
    
   // Merge v1 and v2 to cout
   merge(v1.begin(),v1.end(),v2.begin(),v2.end(),
         ostream_iterator<int>(cout," "));
   cout << endl;

   return 0;
 }

Output:
1 2 3 4
1 2 3 4
1 1 2 2 3 3 4 4
1 1 2 2 3 3 4 4
11 12 13 14 15 16 17 18
11 12 13 14 15 16 17 18
1 1 2 2 3 3 4 4
1 1 2 2 3 3 4 4

If your compiler does not support default template parameters, then you need to always supply the Allocator template argument. For instance, you'll have to write :

vector<int, allocator>

instead of

vector<int>

merge