ranges_is_sorted_until.md

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
}

• forward_iterator[link /reference/iterator/forward_iterator.md]
• sentinel_for[link /reference/iterator/sentinel_for.md]
• ranges::less[link /reference/functional/ranges_less.md]
• identity[link /reference/functional/identity.md]
• indirect_strict_weak_order[link /reference/iterator/indirect_strict_weak_order.md]
• projected[link /reference/iterator/projected.md]
• forward_range[link /reference/ranges/forward_range.md]
• iterator_t[link /reference/ranges/iterator_t.md]
• borrowed_iterator_t[link /reference/ranges/borrowed_iterator_t.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

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

#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

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;

• forward_iterator[link /reference/iterator/forward_iterator.md]
• sentinel_for[link /reference/iterator/sentinel_for.md]
• ranges::less[link /reference/functional/ranges_less.md]
• identity[link /reference/functional/identity.md]
• indirect_strict_weak_order[link /reference/iterator/indirect_strict_weak_order.md]
• projected[link /reference/iterator/projected.md]
• forward_range[link /reference/ranges/forward_range.md]
• iterator_t[link /reference/ranges/iterator_t.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

• Clang: ??
• GCC: 10.1.0 [mark verified]
• ICC: ??
• Visual C++: 2019 Update 10 [mark verified]

参照

• N4861 25 Algorithms library