std::set_symmetric_difference(3)

NAME
std::set_symmetric_difference - std::set_symmetric_difference

Synopsis
   Defined in header <algorithm>
   template< class InputIt1, class InputIt2, class
   OutputIt >
   OutputIt set_symmetric_difference( InputIt1 (until C++20)
   first1, InputIt1 last1,
   InputIt2 first2, InputIt2 last2,
   OutputIt d_first );
   template< class InputIt1, class InputIt2, class
   OutputIt >
   constexpr OutputIt set_symmetric_difference( (since C++20)
   InputIt1 first1, InputIt1 last1,
   InputIt2 first2, InputIt2 last2,
   OutputIt d_first );
   template< class ExecutionPolicy, class
   ForwardIt1, class ForwardIt2,
   class ForwardIt3 >
   ForwardIt3 set_symmetric_difference( (2) (since C++17)
   ExecutionPolicy&& policy,
   ForwardIt1 first1, ForwardIt1 last1,
   ForwardIt2 first2, ForwardIt2 last2,
   ForwardIt3 d_first ); (1)
   template< class InputIt1, class InputIt2, class
   OutputIt, class Compare >
   OutputIt set_symmetric_difference( InputIt1 (until C++20)
   first1, InputIt1 last1,
   InputIt2 first2, InputIt2 last2,
   OutputIt d_first, Compare comp );
   template< class InputIt1, class InputIt2, class
   OutputIt, class Compare >
   constexpr OutputIt set_symmetric_difference( (since C++20)
   InputIt1 first1, InputIt1 last1, (3)
   InputIt2 first2, InputIt2 last2,
   OutputIt d_first, Compare comp );
   template< class ExecutionPolicy, class
   ForwardIt1, class ForwardIt2,
   class ForwardIt3, class Compare >
   ForwardIt3 set_symmetric_difference( (4) (since C++17)
   ExecutionPolicy&& policy,
   ForwardIt1 first1, ForwardIt1 last1,
   ForwardIt2 first2, ForwardIt2 last2,
   ForwardIt3 d_first, Compare comp );
   Computes symmetric difference of two sorted ranges: the elements that are found in
   either of the ranges, but not in both of them are copied to the range beginning at
   d_first. The resulting range is also sorted.
   If some element is found m times in [first1, last1) and n times in [first2, last2),
   it will be copied to d_first exactly std::abs(m-n) times. If m>n, then the last m-n
   of those elements are copied from [first1,last1), otherwise the last n-m elements
   are copied from [first2,last2). The resulting range cannot overlap with either of
   the input ranges.
   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>>
   (until C++20)
   std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
   (since C++20) is true.

Parameters
   first1, last1 - the first sorted range of elements
   first2, last2 - the second sorted range of elements
   policy - the execution policy to use. See execution policy for details.
                   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);
   comp -
                   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.

Type requirements
   -
   InputIt1, InputIt2 must meet the requirements of LegacyInputIterator.
   -
   OutputIt must meet the requirements of LegacyOutputIterator.
   -
   ForwardIt1, ForwardIt2, ForwardIt3 must meet the requirements of
   LegacyForwardIterator.

Return value
   Iterator past the end of the constructed range.

Complexity
   At most \(\scriptsize 2\cdot(N_1+N_2)-1\)2·(N
   1+N
   2)-1 comparisons, where \(\scriptsize N_1\)N
   1 and \(\scriptsize N_2\)N
   2 are std::distance(first1, last1) and std::distance(first2, last2), respectively.

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.

Possible implementation

First version
   template<class InputIt1, class InputIt2, class OutputIt>
   OutputIt set_symmetric_difference(InputIt1 first1, InputIt1 last1,
                        InputIt2 first2, InputIt2 last2,
                        OutputIt d_first)
   {
       while (first1 != last1) {
           if (first2 == last2) return std::copy(first1, last1, d_first);
           if (*first1 < *first2) {
               *d_first++ = *first1++;
           } else {
               if (*first2 < *first1) {
                   *d_first++ = *first2;
               } else {
                   ++first1;
               }
               ++first2;
           }
       }
       return std::copy(first2, last2, d_first);
   }

Second version
   template<class InputIt1, class InputIt2,
            class OutputIt, class Compare>
   OutputIt set_symmetric_difference(InputIt1 first1, InputIt1 last1,
                        InputIt2 first2, InputIt2 last2,
                        OutputIt d_first, Compare comp)
   {
       while (first1 != last1) {
           if (first2 == last2) return std::copy(first1, last1, d_first);
           if (comp(*first1, *first2)) {
               *d_first++ = *first1++;
           } else {
               if (comp(*first2, *first1)) {
                   *d_first++ = *first2;
               } else {
                   ++first1;
               }
               ++first2;
           }
       }
       return std::copy(first2, last2, d_first);
   }

Example
// Run this code
 #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_symDifference;
     std::set_symmetric_difference(
         v1.begin(), v1.end(),
         v2.begin(), v2.end(),
         std::back_inserter(v_symDifference));
     for(int n : v_symDifference)
         std::cout << n << ' ';
 }

Output:
 1 2 3 4 6 8 9 10

See also
                        returns true if one sequence is a subsequence of
   includes another
                        (function template)
   set_difference computes the difference between two sets
                        (function template)
   set_union computes the union of two sets
                        (function template)
   set_intersection computes the intersection of two sets
                        (function template)
   ranges::set_symmetric_difference computes the symmetric difference between two sets
   (C++20) (niebloid)