std::ranges::set_symmetric_difference, std::ranges::set_symmetric_difference_result - cppreference.com

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 result. 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 result exactly │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 the given binary comparison function comp.

2) Same as (1), but uses r1 as the first range and r2 as the second range, as if using ranges::begin(r1) as first1, ranges::end(r1) as last1, ranges::begin(r2) as first2, and ranges::end(r2) as last2.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

{last1, last2, result_last}, where result_last is the end of the constructed range.

At most 2·(N1+N2)-1 comparisons and applications of each projection, where N1 and N2 are ranges::distance(first1, last1) and ranges::distance(first2, last2), respectively.

struct set_symmetric_difference_fn
{
    template<std::input_iterator I1, std::sentinel_for<I1> S1,
             std::input_iterator I2, std::sentinel_for<I2> S2,
             std::weakly_incrementable O, class Comp = ranges::less,
             class Proj1 = std::identity, class Proj2 = std::identity>
    requires std::mergeable<I1, I2, O, Comp, Proj1, Proj2>
    constexpr ranges::set_symmetric_difference_result<I1, I2, O>
        operator()(I1 first1, S1 last1, I2 first2, S2 last2, O result, Comp comp = {},
                   Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        while (!(first1 == last1 or first2 == last2))
        {
            if (std::invoke(comp, std::invoke(proj1, *first1), std::invoke(proj2, *first2)))
            {
                *result = *first1;
                ++first1;
                ++result;
            }
            else if (std::invoke(comp, std::invoke(proj2, *first2),
                                       std::invoke(proj1, *first1)))
            {
                *result = *first2;
                ++first2;
                ++result;
            }
            else
            {
                ++first1;
                ++first2;
            }
        }
        auto res1 {ranges::copy(std::move(first1), std::move(last1), std::move(result))};
        auto res2 {ranges::copy(std::move(first2), std::move(last2), std::move(res1.out))};
        return {std::move(res1.in), std::move(res2.in), std::move(res2.out)};
    }

    template<ranges::input_range R1, ranges::input_range R2,
             std::weakly_incrementable O, class Comp = ranges::less,
             class Proj1 = std::identity, class Proj2 = std::identity>
    requires std::mergeable<ranges::iterator_t<R1>, ranges::iterator_t<R2>,
                            O, Comp, Proj1, Proj2>
    constexpr ranges::set_symmetric_difference_result<
        ranges::borrowed_iterator_t<R1>, ranges::borrowed_iterator_t<R2>, O>
        operator()(R1&& r1, R2&& r2, O result, Comp comp = {},
                   Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        return (*this)(ranges::begin(r1), ranges::end(r1),
                       ranges::begin(r2), ranges::end(r2),
                       std::move(result), std::move(comp),
                       std::move(proj1), std::move(proj2));
    }
};

inline constexpr set_symmetric_difference_fn set_symmetric_difference {};

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>

void visualize_this(const auto& v, int min = 1, int max = 9)
{
    for (auto i {min}; i <= max; ++i)
    {
        std::ranges::binary_search(v, i) ? std::cout << i : std::cout << '.';
        std::cout << ' ';
    }
    std::cout << '\n';
}

int main()
{
    const auto in1 = {1, 3, 4,    6, 7, 9};
    const auto in2 = {1,    4, 5, 6,    9};

    std::vector<int> out {};

    std::ranges::set_symmetric_difference(in1, in2, std::back_inserter(out));

    visualize_this(in1);
    visualize_this(in2);
    visualize_this(out);
}

Output:

1 . 3 4 . 6 7 . 9
1 . . 4 5 6 . . 9
. . 3 . 5 . 7 . .