std:: inplace_merge

Merges two consecutive sorted ranges [ first , middle ) and [ middle , last ) into one sorted range [ first , last ) .

This merge function is stable, which means that for equivalent elements in the original two ranges, the elements from the first range (preserving their original order) precede the elements from the second range (preserving their original order).

If any of the following conditions is satisfied, the behavior is undefined:

• [ first , middle ) or [ middle , last ) is not a valid range .
• The output range overlaps with [ first , middle ) or [ middle , last ) .

Parameters

Complexity

Given \(\scriptsize N\) N as std:: distance ( first, last ) :

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies , std::terminate is called. For any other ExecutionPolicy , the behavior is implementation-defined.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

See the implementations in libstdc++ and libc++ .

Notes

This function attempts to allocate a temporary buffer. If the allocation fails, the less efficient algorithm is chosen.

Example

#include <algorithm>
#include <iostream>
#include <vector>
 
template<class Iter>
void merge_sort(Iter first, Iter last)
{
    if (last - first > 1)
    {
        Iter middle = first + (last - first) / 2;
        merge_sort(first, middle);
        merge_sort(middle, last);
        std::inplace_merge(first, middle, last);
    }
}
 
int main()
{
    std::vector<int> v{8, 2, -2, 0, 11, 11, 1, 7, 3};
    merge_sort(v.begin(), v.end());
    for (const auto& n : v)
        std::cout << n << ' ';
    std::cout << '\n';
}

-2 0 1 2 3 7 8 11 11

See also