## inplace_merge

`Algorithm`

### Summary

Merge two sorted sequences into one.

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, 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.

### 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 <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();
inplace_merge(v5.begin(),mid,v5.end());
// Now use a comparator on v6
mid = v6.begin();
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;
}

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 need to always supply the Allocator template argument. For instance, you'll have to write :

vector<int, allocator,int> >