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ranges_is_sorted_until.md

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is_sorted_until

  • algorithm[meta header]
  • std::ranges[meta namespace]
  • function template[meta id-type]
  • cpp20[meta cpp]
namespace std::ranges {
  template <forward_iterator I,
            sentinel_for<I> S,
            class Proj = identity,
            indirect_strict_weak_order<projected<I, Proj>> Comp = ranges::less>
  constexpr I
    is_sorted_until(I first,
                    S last,
                    Comp comp = {},
                    Proj proj = {}); // (1) C++20

  template <forward_range R,
            class Proj = identity,
            indirect_strict_weak_order<projected<iterator_t<R>, Proj>> Comp = ranges::less>
  constexpr borrowed_iterator_t<R>
    is_sorted_until(R&& r,
                    Comp comp = {},
                    Proj proj = {}); // (2) C++20

  template <execution-policy Ep,
            random_access_iterator I,
            sized_sentinel_for<I> S,
            class Proj = identity,
            indirect_strict_weak_order<projected<I, Proj>> Comp = ranges::less>
  I is_sorted_until(Ep&& exec,
                    I first,
                    S last,
                    Comp comp = {},
                    Proj proj = {}); // (3) C++26

  template <execution-policy Ep,
            sized-random-access-range R,
            class Proj = identity,
            indirect_strict_weak_order<projected<iterator_t<R>, Proj>> Comp = ranges::less>
  borrowed_iterator_t<R>
    is_sorted_until(Ep&& exec,
                    R&& r,
                    Comp comp = {},
                    Proj proj = {}); // (4) C++26
}
  • ranges::less[link /reference/functional/ranges_less.md]
  • indirect_strict_weak_order[link /reference/iterator/indirect_strict_weak_order.md]
  • borrowed_iterator_t[link /reference/ranges/borrowed_iterator_t.md]
  • execution-policy[link /reference/execution/execution-policy.md]
  • random_access_iterator[link /reference/iterator/random_access_iterator.md]
  • sized_sentinel_for[link /reference/iterator/sized_sentinel_for.md]
  • sized-random-access-range[link /reference/ranges/sized-random-access-range.md]

概要

ソート済みか判定し、ソートされていない位置のイテレータを取得する

  • (1): イテレータ範囲を指定する
  • (2): Rangeを直接指定する
  • (3): (1)の並列アルゴリズム版。実行ポリシーを指定する
  • (4): (2)の並列アルゴリズム版。実行ポリシーを指定する

戻り値

distance(first, last) < 2 なら last を返す。そうでない場合、[first,last] の中でソートされている範囲を [first,i) としたとき、そのイテレータ i を返す。

計算量

線形時間

例

基本的な使い方

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

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

  std::cout << std::boolalpha;
  std::cout << "before: is sorted? "
            << (std::ranges::is_sorted_until(v) == v.end()) << std::endl;

  std::sort(v.begin(), v.end());

  std::cout << " after: is sorted? "
            << (std::ranges::is_sorted_until(v) == v.end()) << std::endl;
}
  • std::ranges::is_sorted_until[color ff0000]

出力

before: is sorted? false
 after: is sorted? true

並列アルゴリズムの例 (C++26)

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

int main()
{
  std::vector<int> v = {1, 2, 3, 5, 4, 6};

  // 並列にソート済み範囲の終端を取得する
  auto it = std::ranges::is_sorted_until(std::execution::par, v);

  std::cout << "sorted until: " << *it << std::endl;
  std::cout << "sorted range size: " << (it - v.begin()) << std::endl;
}
  • std::ranges::is_sorted_until[color ff0000]
  • v.begin()[link /reference/vector/vector/begin.md]

出力

sorted until: 4
sorted range size: 4

実装例

struct is_sorted_until_impl {
  template<forward_iterator I, sentinel_for<I> S, class Proj = identity,
           indirect_strict_weak_order<projected<I, Proj>> Comp = ranges::less>
  constexpr I operator()(I first, S last, Comp comp = {}, Proj proj = {}) {
    auto it = first;
    if (it == last || ++it == last)
      return last;
    while (it != last && *first < *it)
      ++first, ++it;
    return it;
  }

  template<forward_range R, class Proj = identity,
           indirect_strict_weak_order<projected<iterator_t<R>, Proj>> Comp = ranges::less>
  constexpr borrowed_iterator_t<R> operator()(R&& r, Comp comp = {}, Proj proj = {}) {
    return (*this)(begin(r), end(r), ref(comp), ref(proj));
  }
};

inline constexpr is_sorted_until_impl is_sorted_until;
  • ranges::less[link /reference/functional/ranges_less.md]
  • indirect_strict_weak_order[link /reference/iterator/indirect_strict_weak_order.md]
  • borrowed_iterator_t[link /reference/ranges/borrowed_iterator_t.md]
  • begin[link /reference/ranges/begin.md]
  • end[link /reference/ranges/end.md]
  • ref[link /reference/functional/ref.md]

バージョン

言語

  • C++20

処理系

参照