std::ranges::is_permutation

template< std::forward_iterator I1, std::sentinel_for<I1> S1,
          std::forward_iterator I2, std::sentinel_for<I2> S2,
          class Proj1 = std::identity, class Proj2 = std::identity,
          std::indirect_equivalence_relation<std::projected<I1, Proj1>,
                                             std::projected<I2, Proj2>>
                                                 Pred = ranges::equal_to >
constexpr bool
    is_permutation( I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {},
                    Proj1 proj1 = {}, Proj2 proj2 = {} );

template< ranges::forward_range R1, ranges::forward_range R2,
          class Proj1 = std::identity, class Proj2 = std::identity,
          std::indirect_equivalence_relation<
              std::projected<ranges::iterator_t<R1>, Proj1>,
              std::projected<ranges::iterator_t<R2>, Proj2>>
                  Pred = ranges::equal_to >
constexpr bool
    is_permutation( R1&& r1, R2&& r2, Pred pred = {},
                    Proj1 proj1 = {}, Proj2 proj2 = {} );

此页面上描述的函数类实体是算法函数对象 (非正式地称为niebloids)，即：

• 调用它们中的任何一个时都不能指定显式模板参数列表。
• 它们都不可通过实参依赖查找可见。
• 当任何一个通过正常非限定查找作为函数调用运算符左侧的名称找到时，实参依赖查找被抑制。

参数

返回值

当范围 [ first1 , last1 ) 是范围 [ first2 , last2 ) 的一个排列时返回 true 。

复杂度

最多进行 \(\scriptsize \mathcal{O}(N^2)\) O(N ² ) 次谓词和投影操作，若序列已相等则精确进行 \(\scriptsize N\) N 次操作，其中 \(\scriptsize N\) N 为 ranges:: distance ( first1, last1 ) 。 但若 ranges:: distance ( first1, last1 ) ! = ranges:: distance ( first2, last2 ) ，则不执行任何谓词和投影操作。

注释

permutation 关系是一种 等价关系 。

ranges::is_permutation 可用于测试场景，例如检验重排算法（如排序、洗牌、分区）的正确性。若 p 是原始序列而 q 是“变异”序列，则 ranges :: is_permutation ( p, q ) == true 表示 q 由与 p “相同”的元素（可能经过排列）构成。

可能的实现

struct is_permutation_fn
{
    template<std::forward_iterator I1, std::sentinel_for<I1> S1,
             std::forward_iterator I2, std::sentinel_for<I2> S2,
             class Proj1 = std::identity, class Proj2 = std::identity,
             std::indirect_equivalence_relation<std::projected<I1, Proj1>,
                                                std::projected<I2, Proj2>>
                                                    Pred = ranges::equal_to>
    constexpr bool operator()(I1 first1, S1 last1, I2 first2, S2 last2,
                              Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        // 跳过公共前缀
        auto ret = std::ranges::mismatch(first1, last1, first2, last2,
                                         std::ref(pred), std::ref(proj1), std::ref(proj2));
        first1 = ret.in1, first2 = ret.in2;
        // 遍历剩余部分，统计每个元素
        // 在 [first1, last1) 中出现的次数与在 [first2, last2) 中出现的次数
        for (auto i {first1}; i != last1; ++i)
        {
            const auto i_proj {std::invoke(proj1, *i)};
            auto i_cmp = [&]<typename T>(T&& t)
            { 
                return std::invoke(pred, i_proj, std::forward<T>(t));
            };
            if (i != ranges::find_if(first1, i, i_cmp, proj1))
                continue; // 此 *i 已被检查
            if (const auto m {ranges::count_if(first2, last2, i_cmp, proj2)};
                m == 0 or m != ranges::count_if(i, last1, i_cmp, proj1))
                return false;
        }
        return true;
    }
    template<ranges::forward_range R1, ranges::forward_range R2,
             class Proj1 = std::identity, class Proj2 = std::identity,
             std::indirect_equivalence_relation<
                 std::projected<ranges::iterator_t<R1>, Proj1>,
                 std::projected<ranges::iterator_t<R2>, Proj2>>
                     Pred = ranges::equal_to>
    constexpr bool operator()(R1&& r1, R2&& r2, Pred pred = {},
                              Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        return (*this)(ranges::begin(r1), ranges::end(r1),
                       ranges::begin(r2), ranges::end(r2),
                       std::move(pred), std::move(proj1), std::move(proj2));
    }
};
inline constexpr is_permutation_fn is_permutation {};

示例

#include <algorithm>
#include <array>
#include <cmath>
#include <iostream>
#include <ranges>
auto& operator<<(auto& os, std::ranges::forward_range auto const& v)
{
    os << "{ ";
    for (const auto& e : v)
        os << e << ' ';
    return os << "}";
}
int main()
{
    static constexpr auto r1 = {1, 2, 3, 4, 5};
    static constexpr auto r2 = {3, 5, 4, 1, 2};
    static constexpr auto r3 = {3, 5, 4, 1, 1};
    static_assert(
        std::ranges::is_permutation(r1, r1) &&
        std::ranges::is_permutation(r1, r2) &&
        std::ranges::is_permutation(r2, r1) &&
        std::ranges::is_permutation(r1.begin(), r1.end(), r2.begin(), r2.end()));
    std::cout
        << std::boolalpha
        << "is_permutation(" << r1 << ", " << r2 << "): "
        << std::ranges::is_permutation(r1, r2) << '\n'
        << "is_permutation(" << r1 << ", " << r3 << "): "
        << std::ranges::is_permutation(r1, r3) << '\n'
        << "is_permutation with custom predicate and projections: "
        << std::ranges::is_permutation(
            std::array {-14, -11, -13, -15, -12},  // 第一范围
            std::array {'F', 'E', 'C', 'B', 'D'},  // 第二范围
            [](int x, int y) { return abs(x) == abs(y); }, // 谓词
            [](int x) { return x + 10; },          // 第一范围的投影
            [](char y) { return int(y - 'A'); })   // 第二范围的投影
        << '\n';
}

is_permutation({ 1 2 3 4 5 }, { 3 5 4 1 2 }): true
is_permutation({ 1 2 3 4 5 }, { 3 5 4 1 1 }): false
is_permutation with custom predicate and projections: true

另请参阅