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Difference between revisions of "cpp/algorithm/is partitioned"

From cppreference.com
< cpp‎ | algorithm
m (fmt)
m (fmt)
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{{dcl end}}
 
{{dcl end}}
  
−
@1@ Returns {{c|true}} if all elements in the range {{tt|[first, last)}} that satisfy the predicate {{tt|p}} appear before all elements that don't. Also returns {{c|true}} if {{tt|[first, last)}} is empty.
+
@1@ Returns {{c|true}} if all elements in the range {{range|first|last}} that satisfy the predicate {{c|p}} appear before all elements that don't. Also returns {{c|true}} if {{range|first|last}} is empty.
  
−
@2@ Same as {{v|1}}, but executed according to {{tt|policy}}. {{cpp/algorithm/parallel overload precondition}}
+
@2@ Same as {{v|1}}, but executed according to {{c|policy}}. {{cpp/algorithm/parallel overload precondition}}
  
 
===Parameters===
 
===Parameters===
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{{par hreq}}
 
{{par hreq}}
 
{{par req named|InputIt|InputIterator}}
 
{{par req named|InputIt|InputIterator}}
−
{{par req named|ForwardIt|ForwardIterator|notes=and its value type must be convertible to UnaryPredicate's argument type}}
+
{{par req named|ForwardIt|ForwardIterator|notes=and its value type must be convertible to UnaryPredicate's argument type.}}
 
{{par req named|UnaryPredicate|Predicate}}
 
{{par req named|UnaryPredicate|Predicate}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
−
{{c|true}} if the range {{tt|[first, last)}} is empty or is partitioned by {{tt|p}}. {{c|false}} otherwise.
+
{{c|true}} if the range {{range|first|last}} is empty or is partitioned by {{c|p}}. {{c|false}} otherwise.
  
 
===Complexity===
 
===Complexity===
−
At most {{tt|std::distance(first, last)}} applications of {{tt|p}}.
+
At most {{c|std::distance(first, last)}} applications of {{c|p}}.
  
 
===Exceptions===
 
===Exceptions===
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===Possible implementation===
 
===Possible implementation===
 
{{eq fun|1=
 
{{eq fun|1=
−
template< class InputIt, class UnaryPredicate >
+
template<class InputIt, class UnaryPredicate>
 
bool is_partitioned(InputIt first, InputIt last, UnaryPredicate p)
 
bool is_partitioned(InputIt first, InputIt last, UnaryPredicate p)
 
{
 
{
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     std::array<int, 9> v {1, 2, 3, 4, 5, 6, 7, 8, 9};
 
     std::array<int, 9> v {1, 2, 3, 4, 5, 6, 7, 8, 9};
  
−
     auto is_even = [](int i){ return i % 2 == 0; };
+
     auto is_even = [](int i) { return i % 2 == 0; };
 
     std::cout.setf(std::ios_base::boolalpha);
 
     std::cout.setf(std::ios_base::boolalpha);
 
     std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
 
     std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';

Revision as of 00:26, 7 April 2023

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
is_partitioned
(C++11)
(C++11)

Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Defined in header <algorithm>
(1)
template< class InputIt, class UnaryPredicate >
bool is_partitioned( InputIt first, InputIt last, UnaryPredicate p );
 (since C++11)
(until C++20)
template< class InputIt, class UnaryPredicate >
constexpr bool is_partitioned( InputIt first, InputIt last, UnaryPredicate p );
 (since C++20)
template< class ExecutionPolicy, class ForwardIt, class UnaryPredicate >

bool is_partitioned( ExecutionPolicy&& policy,

                     ForwardIt first, ForwardIt last, UnaryPredicate p );
 (2) (since C++17)
1) Returns true if all elements in the range [first, last) that satisfy the predicate p appear before all elements that don't. Also returns true if [first, last) is empty.
2) Same as (1), but executed according to policy. This overload participates 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)

Contents

Parameters

first, last - the range of elements to check
policy - the execution policy to use. See execution policy for details.
p - unary predicate which returns ​true for the elements expected to be found in the beginning of the range.

The expression p(v) must be convertible to bool for every argument v of type (possibly const) VT, where VT is the value type of InputIt, regardless of value category, and must not modify v. Thus, a parameter type of VT&is not allowed, nor is VT unless for VT a move is equivalent to a copy(since C++11). ​

Type requirements
-
InputIt must meet the requirements of LegacyInputIterator.
-
ForwardIt must meet the requirements of LegacyForwardIterator. and its value type must be convertible to UnaryPredicate's argument type.
-
UnaryPredicate must meet the requirements of Predicate.

Return value

true if the range [first, last) is empty or is partitioned by p. false otherwise.

Complexity

At most std::distance(first, last) applications of p.

Exceptions

The overload with a template parameter named ExecutionPolicy reports 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.

Possible implementation

template<class InputIt, class UnaryPredicate>
bool is_partitioned(InputIt first, InputIt last, UnaryPredicate p)
{
    for (; first != last; ++first)
        if (!p(*first))
            break;
    for (; first != last; ++first)
        if (p(*first))
            return false;
    return true;
}

Example

Run this code
#include <algorithm>
#include <array>
#include <iostream>
 
int main()
{
    std::array<int, 9> v {1, 2, 3, 4, 5, 6, 7, 8, 9};
 
    auto is_even = [](int i) { return i % 2 == 0; };
    std::cout.setf(std::ios_base::boolalpha);
    std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
 
    std::partition(v.begin(), v.end(), is_even);
    std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
 
    std::reverse(v.begin(), v.end());
    std::cout << std::is_partitioned(v.cbegin(), v.cend(), is_even) << ' ';
    std::cout << std::is_partitioned(v.crbegin(), v.crend(), is_even) << '\n';
}

Output: 

false true false true

See also

 divides a range of elements into two groups
(function template) [edit]
(C++11)
 locates the partition point of a partitioned range
(function template) [edit]
(C++20)
 determines if the range is partitioned by the given predicate
(niebloid)[edit]
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