OutputIt merge( InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2,
class ForwardIt1, class ForwardIt2, class ForwardIt3 >
ForwardIt3 merge( ExecutionPolicy&& policy,
ForwardIt1 first1, ForwardIt1 last1,
ForwardIt2 first2, ForwardIt2 last2,
class OutputIt, class Compare >
OutputIt merge( InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2,
class ForwardIt1, class ForwardIt2,
class ForwardIt3, class Compare >
ForwardIt3 merge( ExecutionPolicy&& policy,
ForwardIt1 first1, ForwardIt1 last1,
ForwardIt2 first2, ForwardIt2 last2,
Merges two sorted ranges [
first1,
last1)
and [
first2,
last2)
into one sorted range beginning at d_first.
If
[
first1,
last1)
or
[
first2,
last2)
is not
sortedwith respect to
operator<(until C++20)std::less{}(since C++20), the behavior is undefined.
3) If [
first1,
last1)
or [
first2,
last2)
is not sorted with respect to comp, the behavior is undefined.
2,4) Same as (1,3), but executed according to policy.
These overloads participate in overload resolution only if all following conditions are satisfied:
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 the output range overlaps with [
first1,
last1)
or [
first2,
last2)
, the behavior is undefined.
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 objects of types InputIt1 and InputIt2 can be dereferenced and then implicitly converted to both Type1 and Type2. â
InputIt1, InputIt2
must meet the requirements of LegacyInputIterator. -ForwardIt1, ForwardIt2, ForwardIt3
must meet the requirements of LegacyForwardIterator. -OutputIt
must meet the requirements of LegacyOutputIterator. -Compare
must meet the requirements of Compare. [edit] Return value
An output iterator to element past the last element copied.
[edit] ComplexityGiven \(\scriptsize N_1\)N1 as std::distance(first1, last1) and \(\scriptsize N_2\)N2 as std::distance(first2, last2):
1)At most
\(\scriptsize N_1+N_2-1\)N1+N2-1comparisons using
operator<(until C++20)std::less{}(since C++20).
2) \(\scriptsize O(N_1+N_2)\)O(N1+N2)comparisons using
operator<(until C++20)std::less{}(since C++20).
3) At most \(\scriptsize N_1+N_2-1\)N1+N2-1 applications of the comparison function comp.
4) \(\scriptsize O(N_1+N_2)\)O(N1+N2) applications of the comparison function comp.
[edit] ExceptionsThe overloads with a template parameter named ExecutionPolicy
report errors as follows:
ExecutionPolicy
is one of the standard policies, std::terminate is called. For any other ExecutionPolicy
, the behavior is implementation-defined.See also the implementations in libstdc++ and libc++.
merge (1)template<class InputIt1, class InputIt2, class OutputIt> OutputIt merge(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, OutputIt d_first) { for (; first1 != last1; ++d_first) { if (first2 == last2) return std::copy(first1, last1, d_first); if (*first2 < *first1) { *d_first = *first2; ++first2; } else { *d_first = *first1; ++first1; } } return std::copy(first2, last2, d_first); }merge (3)
template<class InputIt1, class InputIt2, class OutputIt, class Compare> OutputIt merge(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, OutputIt d_first, Compare comp) { for (; first1 != last1; ++d_first) { if (first2 == last2) return std::copy(first1, last1, d_first); if (comp(*first2, *first1)) { *d_first = *first2; ++first2; } else { *d_first = *first1; ++first1; } } return std::copy(first2, last2, d_first); }[edit] Notes
This algorithm performs a similar task as std::set_union does. Both consume two sorted input ranges and produce a sorted output with elements from both inputs. The difference between these two algorithms is with handling values from both input ranges which compare equivalent (see notes on LessThanComparable). If any equivalent values appeared n times in the first range and m times in the second, std::merge
would output all n + m occurrences whereas std::set_union
would output std::max(n, m) ones only. So std::merge
outputs exactly std::distance(first1, last1) + std::distance(first2, last2) values and std::set_union
may produce fewer.
#include <algorithm> #include <functional> #include <iostream> #include <iterator> #include <random> #include <vector> auto print = [](const auto rem, const auto& v) { std::cout << rem; std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " ")); std::cout << '\n'; }; int main() { // fill the vectors with random numbers std::random_device rd; std::mt19937 mt(rd()); std::uniform_int_distribution<> dis(0, 9); std::vector<int> v1(10), v2(10); std::generate(v1.begin(), v1.end(), std::bind(dis, std::ref(mt))); std::generate(v2.begin(), v2.end(), std::bind(dis, std::ref(mt))); print("Originally:\nv1: ", v1); print("v2: ", v2); std::sort(v1.begin(), v1.end()); std::sort(v2.begin(), v2.end()); print("After sorting:\nv1: ", v1); print("v2: ", v2); // merge std::vector<int> dst; std::merge(v1.begin(), v1.end(), v2.begin(), v2.end(), std::back_inserter(dst)); print("After merging:\ndst: ", dst); }
Possible output:
Originally: v1: 2 6 5 7 4 2 2 6 7 0 v2: 8 3 2 5 0 1 9 6 5 0 After sorting: v1: 0 2 2 2 4 5 6 6 7 7 v2: 0 0 1 2 3 5 5 6 8 9 After merging: dst: 0 0 0 1 2 2 2 2 3 4 5 5 5 6 6 6 7 7 8 9[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior LWG 780 C++98 the merge operation was not defined defined [edit] See also merges two ordered ranges in-placeRetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4