ranges_partial_sort_copy.md

partial_sort_copy

• algorithm[meta header]
• std::ranges[meta namespace]
• function template[meta id-type]
• cpp20[meta cpp]

namespace std::ranges {
  template<input_iterator I1, sentinel_for<I1> S1, random_access_iterator I2, sentinel_for<I2> S2,
           class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity>
    requires indirectly_copyable<I1, I2> && sortable<I2, Comp, Proj2> &&
             indirect_strict_weak_order<Comp, projected<I1, Proj1>, projected<I2, Proj2>>
  constexpr partial_sort_copy_result<I1, I2>
    partial_sort_copy(I1 first, S1 last, I2 result_first, S2 result_last, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}); // (1)

  template<input_range R1, random_access_range R2,
           class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity>
    requires indirectly_copyable<iterator_t<R1>, iterator_t<R2>> &&
             sortable<iterator_t<R2>, Comp, Proj2> &&
             indirect_strict_weak_order<Comp, projected<iterator_t<R1>, Proj1>, projected<iterator_t<R2>, Proj2>>
  constexpr partial_sort_copy_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>>
    partial_sort_copy(R1&& r, R2&& result_r, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {});                              // (2)
}

• partial_sort_copy_result[link ranges_in_out_result.md]
• input_iterator[link /reference/iterator/input_iterator.md]
• random_access_iterator[link /reference/iterator/random_access_iterator.md]
• sentinel_for[link /reference/iterator/sentinel_for.md]
• ranges::less[link /reference/functional/ranges_less.md]
• identity[link /reference/functional/identity.md]
• indirectly_copyable[link /reference/iterator/indirectly_copyable.md]
• indirect_strict_weak_order[link /reference/iterator/indirect_strict_weak_order.md]
• projected[link /reference/iterator/projected.md]
• sortable[link /reference/iterator/sortable.md]
• input_range[link /reference/ranges/input_range.md]
• random_access_range[link /reference/ranges/random_access_range.md]
• iterator_t[link /reference/ranges/iterator_t.md]
• borrowed_iterator_t[link /reference/ranges/borrowed_iterator_t.md]

概要

範囲を部分的にソートした結果を他の範囲にコピーする

• (1): イテレータペアで範囲を指定する
• (2): 範囲を直接指定する

効果

N = min(last - first, result_last - result_first) とする。

[first,last) にある要素の中から、N 個の要素をソート済みの状態で [result_first,result_first + N) に配置する。

戻り値

partial_sort_copy_result {
  .in = last,
  .out = result_first + N
}

• partial_sort_copy_result[link ranges_in_out_result.md]

計算量

ほぼ (last - first) * log(N) 回の比較を行う

例

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

int main()
{
  std::vector<int> v = {3, 1, 4, 2, 5};

  // vから小さい順に2要素取り出す
  std::vector<int> result(2);
  std::ranges::partial_sort_copy(v, result);

  for (int i : result) {
    std::cout << i;
  }
  std::cout << std::endl;
}

• std::ranges::partial_sort_copy[color ff0000]

出力

12

バージョン

言語

• C++20

処理系

• Clang: ??
• GCC: 10.1.0
• ICC: ??
• Visual C++: 2019 Update 10

参照

• N4861 25 Algorithms library