std::set_intersection() algorithm
- od C++20
- od C++17
- do C++17
// (1)
template< class InputIt1, class InputIt2, class OutputIt >
constexpr OutputIt set_intersection( InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2, OutputIt d_first );
// (2)
template< class InputIt1, class InputIt2, class OutputIt, class Compare >
constexpr OutputIt set_intersection( InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2,
OutputIt d_first, Compare comp );
// (3)
template< class ExecutionPolicy, class ForwardIt1,
class ForwardIt2, class ForwardIt3 >
ForwardIt3 set_intersection( ExecutionPolicy&& policy,
ForwardIt1 first1, ForwardIt1 last1,
ForwardIt2 first2, ForwardIt2 last2,
ForwardIt3 d_first );
// (4)
template< class ExecutionPolicy, class ForwardIt1,
class ForwardIt2, class ForwardIt3, class Compare >
ForwardIt3 set_intersection( ExecutionPolicy&& policy,
ForwardIt1 first1, ForwardIt1 last1,
ForwardIt2 first2, ForwardIt2 last2,
ForwardIt3 d_first, Compare comp );
// (1)
template< class InputIt1, class InputIt2, class OutputIt >
OutputIt set_intersection( InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2, OutputIt d_first );
// (2)
template< class InputIt1, class InputIt2, class OutputIt, class Compare >
OutputIt set_intersection( InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2,
OutputIt d_first, Compare comp );
// (3)
template< class ExecutionPolicy, class ForwardIt1,
class ForwardIt2, class ForwardIt3 >
ForwardIt3 set_intersection( ExecutionPolicy&& policy,
ForwardIt1 first1, ForwardIt1 last1,
ForwardIt2 first2, ForwardIt2 last2,
ForwardIt3 d_first );
// (4)
template< class ExecutionPolicy, class ForwardIt1,
class ForwardIt2, class ForwardIt3, class Compare >
ForwardIt3 set_intersection( ExecutionPolicy&& policy,
ForwardIt1 first1, ForwardIt1 last1,
ForwardIt2 first2, ForwardIt2 last2,
ForwardIt3 d_first, Compare comp );
// (1)
template< class InputIt1, class InputIt2, class OutputIt >
OutputIt set_intersection( InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2, OutputIt d_first );
// (2)
template< class InputIt1, class InputIt2, class OutputIt, class Compare >
OutputIt set_intersection( InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2,
OutputIt d_first, Compare comp );
Constructs a sorted range beginning at d_first
consisting of elements that are found in both sorted ranges [first1
; last1
) and [first2
; last2
).
If [first1
; last1
) contains m elements
that are equivalent to each other and [first2
; last2
) contains n
elements that are equivalent to them,
the final std::max(mn, n)
elements will be copied from [first1
; last1
) to the output range, preserving order.
-
(1) Both ranges must be sorted with respect to
operator<
. -
(2) Both ranges must be sorted with respect to
comp
. -
(3 - 4) Same as (1) and (2), but executed according to policy.
Overload ResolutionThese overloads participate in overload resolution only if
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
istrue
. (do C++20)std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
istrue
. (od C++20)
If either of the input ranges is not sorted (using operator<
or comp
, respectively) or overlaps with the output range,
the behavior is undefined
Parameters
first1 last2 | The first sorted range of elements to examine. |
first2 last3 | The second sorted range of elements to examine. |
d_first | The beginning of the destination 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). The signature of the comparison function should be equivalent to the following:
|
Type requirements
InputIt1 InputIt2 | LegacyInputIterator |
ForwardIt1 ForwardIt2 ForwardIt3 | LegacyForwardIterator |
OutputIt1 | LegacyOutputIterator |
Return value
Iterator past the end of the constructed range.
Complexity
Given M
std::distance(first1, last1) and N
as std::distance(first2, last2)
:
- (1, 3) at most 2 * (M + N) - 1 comparisons using
operator<
. - (2, 4) at most 2 * (M + N) - 1 comparison with
comp
.
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 otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory,
std::bad_alloc
is thrown.
Possible implementation
set_intersection(1)
template<class InputIt1, class InputIt2, class OutputIt>
OutputIt set_intersection(InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2, OutputIt d_first)
{
while (first1 != last1 && first2 != last2)
{
if (*first1 < *first2)
++first1;
else
{
if (!(*first2 < *first1))
*d_first++ = *first1++; // *first1 and *first2 are equivalent.
++first2;
}
}
return d_first;
}
set_intersection(2)
template<class InputIt1, class InputIt2, class OutputIt, class Compare>
OutputIt set_intersection(InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2, OutputIt d_first, Compare comp)
{
while (first1 != last1 && first2 != last2)
{
if (comp(*first1, *first2))
++first1;
else
{
if (!comp(*first2, *first1))
*d_first++ = *first1++; // *first1 and *first2 are equivalent.
++first2;
}
}
return d_first;
}
Examples
#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
int main()
{
std::vector<int> v1 {7, 2, 3, 4, 5, 6, 7, 8};
std::vector<int> v2 {5, 7, 9, 7};
std::sort(v1.begin(), v1.end());
std::sort(v2.begin(), v2.end());
std::vector<int> v_intersection;
std::set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(),
std::back_inserter(v_intersection));
for (int n : v_intersection)
std::cout << n << ' ';
std::cout << '\n';
}
5 7 7
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