std::inplace_merge

 

C++

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Concepts library (C++20)

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Regular expressions library (C++11)

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Technical Specifications

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Concepts and utilities: std::Sortable, std::projected, ...
Constrained algorithms: std::ranges::copy, std::ranges::sort, ...
Execution policies (C++17)
is_execution_policy	execution::seqexecution::parexecution::par_unseqexecution::unseq (C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++20)
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	findfind_iffind_if_not (C++11) find_end find_first_of	search search_n lexicographical_compare lexicographical_compare_3way (C++20)
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) shift_leftshift_right (C++20)(C++20) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17) uninitialized_fill	uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy (C++17)	uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) destroy_n (C++17)
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17) compare_3way (C++20)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
C library
qsort	bsearch

 

Defined in header <algorithm>
template< class BidirIt > void inplace_merge( BidirIt first, BidirIt middle, BidirIt last );	(1)
template< class ExecutionPolicy, class BidirIt > void inplace_merge( ExecutionPolicy&& policy, BidirIt first, BidirIt middle, BidirIt last );	(2)	(since C++17)
template< class BidirIt, class Compare> void inplace_merge( BidirIt first, BidirIt middle, BidirIt last, Compare comp );	(3)
template< class ExecutionPolicy, class BidirIt, class Compare> void inplace_merge( ExecutionPolicy&& policy, BidirIt first, BidirIt middle, BidirIt last, Compare comp );	(4)	(since C++17)

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

1) Elements are compared using operator< and the ranges must be sorted with respect to the same.

3) Elements are compared using the given binary comparison function comp and the ranges must be sorted with respect to the same.

2,4) Same as (1,3), but executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

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
policy	-	the execution policy to use. See execution policy for details.
comp	-	comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than (i.e. is ordered before) the second. The signature of the comparison function should be equivalent to the following:  bool cmp(const Type1 &a, const Type2 &b); While the signature does not need to have const &, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1 & is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy (since C++11)). The types Type1 and Type2 must be such that an object of type BidirIt can be dereferenced and then implicitly converted to both of them. ​
Type requirements
- BidirIt must meet the requirements of ValueSwappable and LegacyBidirectionalIterator.
- The type of dereferenced BidirIt must meet the requirements of MoveAssignable and MoveConstructible.

Return value

(none)

Complexity

Given N = std::distance(first, last)},

1,3) Exactly N-1 comparisons if enough additional memory is available. If the memory is insufficient, O(N log N) comparisons.

2,4) O(N log N) comparisons.

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.

Notes

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

Example

The following code is an implementation of merge sort.

Run this code

#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

See also

merge	merges two sorted ranges (function template)
sort	sorts a range into ascending order (function template)
stable_sort	sorts a range of elements while preserving order between equal elements (function template)