## inplace_merge

    Algorithm

- Summary
- Data Type and Member Function Indexes
- Synopsis
- Description
- Complexity
- Example
- Warnings
- See Also

### Summary

Merges two sorted sequences into one.

### Data Type and Member Function Indexes
(exclusive of constructors and destructors)

None

### Synopsis

    #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);

### Description

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, which means that 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.

### Complexity

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.

### Example

    //
    // merge.cpp
    //
     #include <algorithm>
     #include <vector>
     #include <functional>
     #include <iostream>
     using namespace std;

     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,char> 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,char>(cout," "));
       cout << endl;
       return 0;
     }

Program 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

### Warnings

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

`vector<int, allocator,int> >`

instead of:

`vector<int>`

If your compiler does not support namespaces, then you do not need the using declaration for `std`.

### See Also

merge

Copyright (c) 1998, Rogue Wave Software, Inc.
Send mail to report errors or comment on the documentation.
OEM Release, June 1998