ranges_search.md

search

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

namespace std::ranges {
  template <forward_iterator I1,
            sentinel_for<I1> S1,
            forward_iterator I2,
            sentinel_for<I2> S2,
            class Pred = ranges::equal_to,
            class Proj1 = identity,
            class Proj2 = identity>
    requires indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
  constexpr subrange<I1>
    search(I1 first1,
           S1 last1,
           I2 first2,
           S2 last2,
           Pred pred = {},
           Proj1 proj1 = {},
           Proj2 proj2 = {}); // (1) C++20

  template <forward_range R1,
            forward_range R2,
            class Pred = ranges::equal_to,
            class Proj1 = identity,
            class Proj2 = identity>
    requires indirectly_comparable<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
  constexpr borrowed_subrange_t<R1>
    search(R1&& r1,
           R2&& r2,
           Pred pred = {},
           Proj1 proj1 = {},
           Proj2 proj2 = {}); // (2) C++20
}

• forward_iterator[link /reference/iterator/forward_iterator.md]
• sentinel_for[link /reference/iterator/sentinel_for.md]
• ranges::equal_to[link /reference/functional/ranges_equal_to.md]
• identity[link /reference/functional/identity.md]
• indirectly_comparable[link /reference/iterator/indirectly_comparable.md]
• subrange[link /reference/ranges/subrange.md]
• forward_range[link /reference/ranges/forward_range.md]
• iterator_t[link /reference/ranges/iterator_t.md]
• borrowed_subrange_t[link /reference/ranges/borrowed_subrange_t.md]

概要

あるシーケンスの中から、特定のサブシーケンスを探す

• (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

• (1) :
  • [first1,last1 - (last2 - first2)) 内のイテレータ i があるとき、0 以上 last2 - first2 未満の整数 n について、それぞれ invoke(pred, invoke(proj1, *(i + n)), invoke(proj2, *(first2 + n))) であるようなサブシーケンスを探し、見つかった最初のサブシーケンスを返す。
  • そのようなイテレータが見つからない場合は {last1, last1} を返し、[first2,last2) が空である場合には {first1, first1} を返す。
• (2): first1 = begin(r1), last1 = end(r1), first2 = begin(r2), last2 = end(r2)の下で(1)と等しい。

計算量

最大で (last1 - first1) * (last2 - first2) 回の、対応する比較もしくは述語が適用される

例

#include <algorithm>
#include <iostream>
#include <vector>
#include <list>
#include <ranges>

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

  // 1,2 と連続している最初のシーケンスを探す
  std::ranges::subrange sr = std::ranges::search(v, ls);
  // v[0] の位置を指すイテレータが見つかる。
  if (sr.empty()) {
    std::cout << "not found" << std::endl;
  } else {
    std::cout << "found: index==" << std::distance(v.begin(), sr.begin()) << std::endl;
  }
}

• std::ranges::search[color ff0000]

出力

found: index==0

実装例

struct search_impl {
  template<forward_iterator I1, sentinel_for<I1> S1, forward_iterator I2,
  sentinel_for<I2> S2, class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
    requires indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
  constexpr subrange<I1> operator()(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const {
    for ( ; first1 != last1; ++first1) {
      I1 p1 = first1;
      I2 p2 = first2;
      while (true) {
        if (p2 == last2) return {first1, p1};
        if (p1 == last1) return {last1, last1};
        if (!invoke(pred, invoke(proj1, *p1), invoke(proj2, *p2))) break;
        ++p1, ++p2;
      }
    }
  }

  template<forward_range R1, forward_range R2, class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
    requires indirectly_comparable<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
  constexpr borrowed_subrange_t<R1> operator()(R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const {
    return (*this)(begin(r1), end(r1), begin(r2), end(r2), ref(pred), ref(proj1), ref(proj2));
  }
};

inline constexpr search_impl search;

• forward_iterator[link /reference/iterator/forward_iterator.md]
• sentinel_for[link /reference/iterator/sentinel_for.md]
• ranges::equal_to[link /reference/functional/ranges_equal_to.md]
• identity[link /reference/functional/identity.md]
• indirectly_comparable[link /reference/iterator/indirectly_comparable.md]
• subrange[link /reference/ranges/subrange.md]
• forward_range[link /reference/ranges/forward_range.md]
• iterator_t[link /reference/ranges/iterator_t.md]
• borrowed_subrange_t[link /reference/ranges/borrowed_subrange_t.md]
• invoke[link /reference/functional/invoke.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
• ICC: ??
• Visual C++: 2019 Update 10

参照

• N4861 25 Algorithms library