std::set_intersection
Defined in header <algorithm>
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template< class InputIt1, class InputIt2, class OutputIt > OutputIt set_intersection( InputIt1 first1, InputIt1 last1, |
(1) | |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class ForwardIt3 > ForwardIt3 set_intersection( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1, |
(2) | (since C++17) |
template< class InputIt1, class InputIt2, class OutputIt, class Compare > |
(3) | |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class ForwardIt3, class Compare > |
(4) | (since C++17) |
Constructs a sorted range beginning at d_first
consisting of elements that are found in both sorted ranges [first1, last1)
and [first2, last2)
. If some element is found m
times in [first1, last1)
and n
times in [first2, last2)
, the first std::min(m, n) elements will be copied from the first range to the destination range. The order of equivalent elements is preserved. The resulting range cannot overlap with either of the input ranges.
operator<
and the ranges must be sorted with respect to the same.comp
and the ranges must be sorted with respect to the same.policy
. This overload only participates in overload resolution if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is trueParameters
first1, last1 | - | the first range of elements to examine |
first2, last2 | - | the second range of elements to examine |
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); The signature does not need to have const &, but the function object must not modify the objects passed to it. |
Type requirements | ||
-InputIt1, InputIt2 must meet the requirements of InputIterator .
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-OutputIt must meet the requirements of OutputIterator .
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-ForwardIt1, ForwardIt2, ForwardIt3 must meet the requirements of ForwardIterator .
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Return value
Iterator past the end of the constructed range.
Complexity
At most 2·(N1+N2-1) comparisons, where N1 = std::distance(first1, last1) and N2 = std::distance(first2, last2).
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 three 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
First version |
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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++; } ++first2; } } return d_first; } |
Second version |
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++; } ++first2; } } return d_first; } |
Example
#include <iostream> #include <vector> #include <algorithm> #include <iterator> int main() { std::vector<int> v1{1,2,3,4,5,6,7,8}; std::vector<int> v2{ 5, 7, 9,10}; 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 << ' '; }
Output:
5 7
See also
computes the union of two sets (function template) |