Difference between revisions of "cpp/algorithm/includes"

Latest revision as of 19:41, 6 April 2024

Defined in header `<algorithm>`
template< class InputIt1, class InputIt2 > bool includes( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2 );	(1)	(constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > bool includes( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2, ForwardIt2 last2 );	(2)	(since C++17)
template< class InputIt1, class InputIt2, class Compare > bool includes( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, Compare comp );	(3)	(constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class Compare > bool includes( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2, ForwardIt2 last2, Compare comp );	(4)	(since C++17)

Returns true if the sorted range [first2, last2) is a subsequence of the sorted range [first1, last1) (a subsequence need not be contiguous).

1) If [first1, last1) or [first2, last2) is not sorted with respect to operator<(until C++20)std::less{}(since C++20), the behavior is undefined.

3) If [first1, last1) or [first2, last2) is not sorted with respect to comp, the behavior is undefined.

2,4) Same as (1,3), but executed according to policy.

These overloads participate in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.	(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.	(since C++20)

first1, last1	-	the sorted range of elements to examine
first2, last2	-	the sorted range of elements to search for
policy	-	the execution policy to use. See execution policy for details.
comp	-	comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if the first argument is less than (i.e. is ordered before) the second. The signature of the comparison function should be equivalent to the following: bool cmp(const Type1& a, const Type2& b); While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) `Type1` and `Type2` regardless of value category (thus, `Type1&` is not allowed, nor is `Type1` unless for `Type1` a move is equivalent to a copy(since C++11)). The types Type1 and Type2 must be such that an object of type InputIt can be dereferenced and then implicitly converted to both of them.
Type requirements
- `InputIt1, InputIt2` must meet the requirements of LegacyInputIterator.
- `ForwardIt1, ForwardIt2` must meet the requirements of LegacyForwardIterator.
- `Compare` must meet the requirements of Compare.

[edit] Return value

true if [first2, last2) is a subsequence of [first1, last1); otherwise false.

An empty sequence is a subsequence of any sequence, so true is returned if [first2, last2) is empty.

[edit] Complexity

Given $\scriptsize N_1$ $N 1$ as std::distance(first1, last1) and $\scriptsize N_2$ $N 2$ as std::distance(first2, last2):

1,2) At most

2\cdot(N 1 +N 2)-1

comparisons using operator<(until C++20)std::less{}(since C++20).

3,4) At most

2\cdot(N 1 +N 2)-1

applications of the comparison function comp.

[edit] Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
If the algorithm fails to allocate memory, std::bad_alloc is thrown.

[edit] Possible implementation

include (1)

template<class InputIt1, class InputIt2>
bool includes(InputIt1 first1, InputIt1 last1,
              InputIt2 first2, InputIt2 last2)
{
    for (; first2 != last2; ++first1)
    {
        if (first1 == last1 || *first2 < *first1)
            return false;
        if (!(*first1 < *first2))
            ++first2;
    }
    return true;
}

include (3)

template<class InputIt1, class InputIt2, class Compare>
bool includes(InputIt1 first1, InputIt1 last1,
              InputIt2 first2, InputIt2 last2, Compare comp)
{
    for (; first2 != last2; ++first1)
    {
        if (first1 == last1 || comp(*first2, *first1))
            return false;
        if (!comp(*first1, *first2))
            ++first2;
    }
    return true;
}

[edit] Example

Run this code

#include <algorithm>
#include <cctype>
#include <iostream>
 
template<class Os, class Co>
Os& operator<<(Os& os, const Co& v)
{
    for (const auto& i : v)
        os << i << ' ';
    return os << '\t';
}
 
int main()
{
    const auto
        v1 = {'a', 'b', 'c', 'f', 'h', 'x'},
        v2 = {'a', 'b', 'c'},
        v3 = {'a', 'c'},
        v4 = {'a', 'a', 'b'},
        v5 = {'g'},
        v6 = {'a', 'c', 'g'},
        v7 = {'A', 'B', 'C'};
 
    auto no_case = [](char a, char b) { return std::tolower(a) < std::tolower(b); };
 
    std::cout
    << v1 << "\nincludes:\n" << std::boolalpha
    << v2 << ": " << std::includes(v1.begin(), v1.end(), v2.begin(), v2.end()) << '\n'
    << v3 << ": " << std::includes(v1.begin(), v1.end(), v3.begin(), v3.end()) << '\n'
    << v4 << ": " << std::includes(v1.begin(), v1.end(), v4.begin(), v4.end()) << '\n'
    << v5 << ": " << std::includes(v1.begin(), v1.end(), v5.begin(), v5.end()) << '\n'
    << v6 << ": " << std::includes(v1.begin(), v1.end(), v6.begin(), v6.end()) << '\n'
    << v7 << ": " << std::includes(v1.begin(), v1.end(), v7.begin(), v7.end(), no_case)
          << " (case-insensitive)\n";
}

Output:

a b c f h x
includes:
a b c   : true
a c     : true
a a b   : false
g       : false
a c g   : false
A B C   : true (case-insensitive)

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 1205	C++98	the return value was unclear if `[`first2`,` last2`)` is empty	returns true in this case

[edit] See also

set_difference	computes the difference between two sets (function template) [edit]
search	searches for the first occurrence of a range of elements (function template) [edit]
ranges::includes (C++20)	returns true if one sequence is a subsequence of another (niebloid)[edit]

@@ Line 2: / Line 2: @@
 {{cpp/algorithm/navbar}}
 {{dcl begin}}
-{{dcl header | algorithm}}
+{{dcl header|algorithm}}
-{{dcl | num=1 |
+{{dcla|num=1|notes={{mark constexpr since c++20}}|
 template< class InputIt1, class InputIt2 >
 bool includes( InputIt1 first1, InputIt1 last1,
                 InputIt2 first2, InputIt2 last2 );
 }}
-{{dcl | num=2 |
+{{dcl|num=2|since=c++17|
-template< class InputIt1, class InputIt2 >
+template< class ExecutionPolicy,
+          class ForwardIt1, class ForwardIt2 >
+bool includes( ExecutionPolicy&& policy,
+               ForwardIt1 first1, ForwardIt1 last1,
+               ForwardIt2 first2, ForwardIt2 last2 );
+}}
+{{dcla|num=3|notes={{mark constexpr since c++20}}|
+template< class InputIt1, class InputIt2, class Compare >
 bool includes( InputIt1 first1, InputIt1 last1,
                 InputIt2 first2, InputIt2 last2, Compare comp );
+}}
+{{dcl|num=4|since=c++17|
+template< class ExecutionPolicy,
+          class ForwardIt1, class ForwardIt2, class Compare >
+bool includes( ExecutionPolicy&& policy,
+               ForwardIt1 first1, ForwardIt1 last1,
+               ForwardIt2 first2, ForwardIt2 last2, Compare comp );
 }}
 {{dcl end}}
-Returns {{c|true}} if every element from the sorted range {{tt|[first2, last2)}} is found within the sorted range {{tt|[first1, last1)}}. Also returns {{c|true}} if {{tt|[first2, last2)}} is empty.
+Returns {{c|true}} if the sorted range {{range|first2|last2}} is a {{enwiki|subsequence}} of the sorted range {{range|first1|last1}} (a subsequence need not be contiguous).
-The first version expects both ranges to be sorted with {{c|operator<}}, the second version expects them to be sorted with the given comparison function {{tt|comp}}.
+@1@ If {{range|first1|last1}} or {{range|first2|last2}} is not {{rlp|/#Requirements|sorted}} with respect to {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}, the behavior is undefined.
+@3@ If {{range|first1|last1}} or {{range|first2|last2}} is not sorted with respect to {{c|comp}}, the behavior is undefined.
+@2,4@ Same as {{v|1,3}}, but executed according to {{c|policy}}.
+@@ {{cpp/algorithm/parallel overload precondition|plural=yes}}
 ===Parameters===
 {{par begin}}
-{{par | first1, last1 | the sorted range of elements to examine}}
+{{par|first1, last1|the sorted range of elements to examine}}
-{{par | first2, last2 | the sorted range of elements to search for}}
+{{par|first2, last2|the sorted range of elements to search for}}
-{{par cmp ord | comp | p1=InputIt}}
+{{par exec pol}}
+{{par cmp ord|comp|p1=InputIt}}
 {{par hreq}}
-{{par req concept | InputIt | InputIterator}}
+{{par req named|InputIt1, InputIt2|InputIterator}}
+{{par req named|ForwardIt1, ForwardIt2|ForwardIterator}}
+{{par req named|Compare|Compare}}
 {{par end}}
 ===Return value===
-{{c|true}} if every element from {{tt|[first2, last2)}} is a member of {{tt|[first, last)}}.
+{{c|true}} if {{range|first2|last2}} is a subsequence of {{range|first1|last1}}; otherwise {{c|false}}.
+An empty sequence is a subsequence of any sequence, so {{c|true}} is returned if {{range|first2|last2}} is empty.
 ===Complexity===
-At most {{math|2&middot;(N<sub>1</sub>+N<sub>2</sub>-1)}} comparisons, where {{math|N<sub>1</sub>}} {{c|{{=}} std::distance(first1, last1)}} and {{math|N<sub>2</sub>}} {{c|{{=}} std::distance(first2, last2)}}.
+Given {{mathjax-or|\(\scriptsize N_1\)|N{{su|b=1}}}} as {{c|std::distance(first1, last1)}} and {{mathjax-or|\(\scriptsize N_2\)|N{{su|b=2}}}} as {{c|std::distance(first2, last2)}}:
+@1,2@ At most {{mathjax-or|\(\scriptsize 2 \cdot (N_1+N_2)-1\)|2⋅(N{{su|b=1}}+N{{su|b=2}})-1}} comparisons using {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
+@3,4@ At most {{mathjax-or|\(\scriptsize 2 \cdot (N_1+N_2)-1\)|2⋅(N{{su|b=1}}+N{{su|b=2}})-1}} applications of the comparison function {{c|comp}}.
+===Exceptions===
+{{cpp/algorithm/parallel exceptions reporting behavior|singular=no}}
 ===Possible implementation===
-{{eq fun
+{{eq impl
- | 1=
+|title1=include (1)|ver1=1|1=
 template<class InputIt1, class InputIt2>
 bool includes(InputIt1 first1, InputIt1 last1,
@@ Line 45: / Line 76: @@
          if (first1 == last1 {{!!}} *first2 < *first1)
              return false;
-         if ( !(*first1 < *first2) )
+         if (!(*first1 < *first2))
              ++first2;
      }
      return true;
 }
- | 2=
+|title2=include (3)|ver2=3|2=
-template<class InputIt1, class InputIt2>
+template<class InputIt1, class InputIt2, class Compare>
 bool includes(InputIt1 first1, InputIt1 last1,
                InputIt2 first2, InputIt2 last2, Compare comp)
@@ Line 68: / Line 99: @@
 ===Example===
 {{example
- |
+||code=
- | code=
-#include <iostream>
 #include <algorithm>
 #include <cctype>
-#include <vector>
+#include <iostream>
+template<class Os, class Co>
+Os& operator<<(Os& os, const Co& v)
+{
+    for (const auto& i : v)
+        os << i << ' ';
+    return os << '\t';
+}
 int main()
 {
-  std::vector<char> v1 {'a', 'b', 'c', 'f', 'h', 'x'};
+    const auto
-  std::vector<char> v2 {'a', 'b', 'c'};
+        v1 = {'a', 'b', 'c', 'f', 'h', 'x'},
-  std::vector<char> v3 {'a', 'c'};
+        v2 = {'a', 'b', 'c'},
-  std::vector<char> v4 {'g'};
+        v3 = {'a', 'c'},
-  std::vector<char> v5 {'a', 'c', 'g'};
+        v4 = {'a', 'a', 'b'},
-  std::vector<char> v6 {'A', 'B', 'C'};
+        v5 = {'g'},
+        v6 = {'a', 'c', 'g'},
+        v7 = {'A', 'B', 'C'};
-  for (auto i : v1) std::cout << i << ' ';
+    auto no_case = [](char a, char b) { return std::tolower(a) < std::tolower(b); };
-  std::cout << "includes:\n";
-  for (auto i : v2) std::cout << i << ' ';
+    std::cout
-  std::cout << ": " << std::includes(v1.begin(), v1.end(), v2.begin(), v2.end()) << '\n';
+    << v1 << "\nincludes:\n" << std::boolalpha
-  for (auto i : v3) std::cout << i << ' ';
+    << v2 << ": " << std::includes(v1.begin(), v1.end(), v2.begin(), v2.end()) << '\n'
-  std::cout << ": " << std::includes(v1.begin(), v1.end(), v3.begin(), v3.end()) << '\n';
+    << v3 << ": " << std::includes(v1.begin(), v1.end(), v3.begin(), v3.end()) << '\n'
-  for (auto i : v4) std::cout << i << ' ';
+    << v4 << ": " << std::includes(v1.begin(), v1.end(), v4.begin(), v4.end()) << '\n'
-  std::cout << ": " << std::includes(v1.begin(), v1.end(), v4.begin(), v4.end()) << '\n';
+    << v5 << ": " << std::includes(v1.begin(), v1.end(), v5.begin(), v5.end()) << '\n'
-  for (auto i : v5) std::cout << i << ' ';
+     << v6 << ": " << std::includes(v1.begin(), v1.end(), v6.begin(), v6.end()) << '\n'
-  std::cout << ": " << std::includes(v1.begin(), v1.end(), v5.begin(), v5.end()) << '\n';
+    << v7 << ": " << std::includes(v1.begin(), v1.end(), v7.begin(), v7.end(), no_case)
+          << " (case-insensitive)\n";
-  auto cmp_nocase = [](char a, char b) {
-     return std::tolower(a) < std::tolower(b);
-  };
-  for (auto i : v6) std::cout << i << ' ';
-  std::cout << ": "
-            << std::includes(v1.begin(), v1.end(), v6.begin(), v6.end(), cmp_nocase)
-            << '\n';
 }
- | output=
+|output=
-a b c f h x includes:
+a b c f h x
-a b c : 1
+includes:
-a c : 1
+a b c   : true
-g : 0
+a c     : true
-a c g : 0
+a a b   : false
-A B C : 1
+g       : false
+a c g   : false
+A B C   : true (case-insensitive)
 }}
+===Defect reports===
+{{dr list begin}}
+{{dr list item|wg=lwg|dr=1205|std=C++98|before=the return value was unclear if {{range|first2|last2}} is empty|after=returns {{c|true}} in this case}}
+{{dr list end}}
 ===See also===
 {{dsc begin}}
-{{dsc inc | cpp/algorithm/dsc set_difference}}
+{{dsc inc|cpp/algorithm/dsc set_difference}}
-{{dsc inc | cpp/algorithm/dsc search}}
+{{dsc inc|cpp/algorithm/dsc search}}
+{{dsc inc|cpp/algorithm/ranges/dsc includes}}
 {{dsc end}}
-[[de:cpp/algorithm/includes]]
+{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
-[[es:cpp/algorithm/includes]]
-[[fr:cpp/algorithm/includes]]
-[[it:cpp/algorithm/includes]]
-[[ja:cpp/algorithm/includes]]
-[[pt:cpp/algorithm/includes]]
-[[ru:cpp/algorithm/includes]]
-[[zh:cpp/algorithm/includes]]

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Difference between revisions of "cpp/algorithm/includes"

Latest revision as of 19:41, 6 April 2024

Contents

[edit] Parameters