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std::inplace_merge

From cppreference.com
 
 
 
Defined in header <algorithm>
template< class BidirectionalIterator >

void inplace_merge( BidirectionalIterator first,
                    BidirectionalIterator middle,

                    BidirectionalIterator last );
(1)
template< class BidirectionalIterator, class Compare>

void inplace_merge( BidirectionalIterator first,
                    BidirectionalIterator middle,
                    BidirectionalIterator last,

                    Compare comp );
(2)

Merges two consecutive sorted ranges [first, middle) and [middle, last) into one sorted range [first, last). The order of equal elements is guaranteed to be preserved. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.

Contents

[edit] Parameters

first - the beginning of the first sorted range
middle - the end of the first sorted range and the beginning of the second
last - the end of the second sorted range
comp - comparison function which returns ​true if the first argument is less than the second.

The signature of the comparison function should be equivalent to the following:

bool cmp(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The types  Type1 and  Type2 must be such that an object of type BidirectionalIterator can be dereferenced and then implicitly converted to both of them. ​

[edit] Return value

(none)

[edit] Complexity

Exctly N-1 comparisons if enough additional memory is available, otherwise N·log(N) where N = std::distance(first, last).

[edit] Example

The following code is an implementation of merge sort.

#include <vector>
#include <iostream>
#include <algorithm>
 
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(auto n : v) {
        std::cout << n << ' ';
    }
    std::cout << '\n';
}

Output:

-2 0 1 2 3 7 8 11 11

[edit] See also

merges two sorted ranges
(function template) [edit]
sorts a range into ascending order
(function template) [edit]
sorts a range of elements while preserving order between equal elements
(function template) [edit]