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

From cppreference.com
< cpp‎ | algorithm
m (.)
(Wording update.)
 
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{{dcl begin}}
 
{{dcl begin}}
 
{{dcl header|algorithm}}
 
{{dcl header|algorithm}}
−
{{dcl rev multi|num=1|anchor=1|since1=c++11|until1=c++20|dcl1=
+
{{dcla|num=1|since=c++11|notes={{mark constexpr since c++20}}|
 
template< class ForwardIt >
 
template< class ForwardIt >
 
bool is_sorted( ForwardIt first, ForwardIt last );
 
bool is_sorted( ForwardIt first, ForwardIt last );
−
|dcl2=
 
−
template< class ForwardIt >
 
−
constexpr bool is_sorted( ForwardIt first, ForwardIt last );
 
 
}}
 
}}
−
{{dcl|since=c++17|until=|num=2|1=
+
{{dcl|num=2|since=c++17|
 
template< class ExecutionPolicy, class ForwardIt >
 
template< class ExecutionPolicy, class ForwardIt >
−
bool is_sorted( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last );
+
bool is_sorted( ExecutionPolicy&& policy,
 +
                ForwardIt first, ForwardIt last );
 
}}
 
}}
−
{{dcl rev multi|num=3|anchor=3|since1=c++11|until1=c++20|dcl1=
+
{{dcla|num=3|since=c++11|notes={{mark constexpr since c++20}}|
 
template< class ForwardIt, class Compare >
 
template< class ForwardIt, class Compare >
 
bool is_sorted( ForwardIt first, ForwardIt last, Compare comp );
 
bool is_sorted( ForwardIt first, ForwardIt last, Compare comp );
−
|dcl2=
 
−
template< class ForwardIt, class Compare >
 
−
constexpr bool is_sorted( ForwardIt first, ForwardIt last, Compare comp );
 
 
}}
 
}}
−
{{dcl|since=c++17|until=|num=4|1=
+
{{dcl|num=4|since=c++17|
 
template< class ExecutionPolicy, class ForwardIt, class Compare >
 
template< class ExecutionPolicy, class ForwardIt, class Compare >
−
bool is_sorted( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last,
+
bool is_sorted( ExecutionPolicy&& policy,
−
                Compare comp );
+
                ForwardIt first, ForwardIt last, Compare comp );
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
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Checks if the elements in range {{range|first|last}} are sorted in non-descending order.
 
Checks if the elements in range {{range|first|last}} are sorted in non-descending order.
  
−
A sequence is sorted with respect to a comparator {{c|comp}} if for any iterator {{tt|it}} pointing to the sequence and any non-negative integer {{tt|n}} such that {{c|it + n}} is a valid iterator pointing to an element of the sequence, {{c|comp(*(it + n), *it)}} evaluates to {{c|false}}.
+
@1@ Checks if the elements are {{rlp|/#Requirements|sorted}} with respect to {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
  
−
@1@ Elements are compared using {{tt|operator<}}.
+
@3@ Checks if the elements are sorted with respect to {{c|comp}}.
−
@3@ Elements are compared using the given binary comparison function {{c|comp}}.
+
 
−
@2,4@ Same as {{v|1,3}}, but executed according to {{c|policy}}. {{cpp/algorithm/parallel overload precondition|plural=true}}
+
@2,4@ Same as {{v|1,3}}, but executed according to {{c|policy}}.
 +
@@ {{cpp/algorithm/parallel overload precondition|plural=yes}}
  
 
===Parameters===
 
===Parameters===
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{{par hreq}}
 
{{par hreq}}
 
{{par req named|ForwardIt|ForwardIterator}}
 
{{par req named|ForwardIt|ForwardIterator}}
 +
{{par req named|Compare|Compare}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
−
{{c|true}} if the elements in the range are sorted in non-descending order.
+
{{c|true}} if the elements in the range are sorted in non-descending order, {{c|false}} otherwise.
  
 
===Complexity===
 
===Complexity===
−
Linear in the distance between {{c|first}} and {{c|last}}.
+
Given {{mathjax-or|\(\scriptsize N\)|N}} as {{c|std::distance(first, last)}}:
 +
 
 +
@1,2@ {{mathjax-or|\(\scriptsize O(N)\)|O(N)}} comparisons using {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
 +
 
 +
@3,4@ {{mathjax-or|\(\scriptsize O(N)\)|O(N)}} applications of the comparator {{c|comp}}.
  
 
===Exceptions===
 
===Exceptions===
−
{{cpp/algorithm/parallel_exceptions_reporting_behavior|singular=no}}
+
{{cpp/algorithm/parallel exceptions reporting behavior|singular=no}}
  
 
===Possible implementation===
 
===Possible implementation===
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     v.push_back(42);
 
     v.push_back(42);
 
     assert(std::is_sorted(v.cbegin(), v.cend()) && "a range of size 1 is always sorted");
 
     assert(std::is_sorted(v.cbegin(), v.cend()) && "a range of size 1 is always sorted");
−
 
+
   
 
     int data[] = {3, 1, 4, 1, 5};
 
     int data[] = {3, 1, 4, 1, 5};
 
     assert(not std::is_sorted(std::begin(data), std::end(data)));
 
     assert(not std::is_sorted(std::begin(data), std::end(data)));
−
 
+
   
 
     std::sort(std::begin(data), std::end(data));
 
     std::sort(std::begin(data), std::end(data));
 
     assert(std::is_sorted(std::begin(data), std::end(data)));
 
     assert(std::is_sorted(std::begin(data), std::end(data)));

Latest revision as of 19:38, 2 April 2024

 
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
Sorting operations
is_sorted
(C++11)
(C++11)

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>
template< class ForwardIt >
bool is_sorted( ForwardIt first, ForwardIt last );
 (1) (since C++11)
(constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt >

bool is_sorted( ExecutionPolicy&& policy,

                ForwardIt first, ForwardIt last );
 (2) (since C++17)
template< class ForwardIt, class Compare >
bool is_sorted( ForwardIt first, ForwardIt last, Compare comp );
 (3) (since C++11)
(constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt, class Compare >

bool is_sorted( ExecutionPolicy&& policy,

                ForwardIt first, ForwardIt last, Compare comp );
 (4) (since C++17)

Checks if the elements in range [first, last) are sorted in non-descending order.

1) Checks if the elements are sorted with respect to operator<(until C++20)std::less{}(since C++20).
3) Checks if the elements are sorted with respect to comp.
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)

Contents

[edit] Parameters

first, last - the range of elements to examine
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 ForwardIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
-
ForwardIt must meet the requirements of LegacyForwardIterator.
-
Compare must meet the requirements of Compare.

[edit] Return value

true if the elements in the range are sorted in non-descending order, false otherwise.

[edit] Complexity

Given N as std::distance(first, last):

1,2) O(N) comparisons using operator<(until C++20)std::less{}(since C++20).
3,4) O(N) applications of the comparator 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

See also the implementations in libstdc++ and libc++.


is_sorted (1) 
template<class ForwardIt>
bool is_sorted(ForwardIt first, ForwardIt last)
{
    return std::is_sorted_until(first, last) == last;
}
is_sorted (3) 
template<class ForwardIt, class Compare>
bool is_sorted(ForwardIt first, ForwardIt last, Compare comp)
{
    return std::is_sorted_until(first, last, comp) == last;
}

[edit] Notes

std::is_sorted returns true for empty ranges and ranges of length one.

[edit] Example

Run this code
#include <algorithm>
#include <cassert>
#include <functional>
#include <iterator>
#include <vector>
 
int main()
{
    std::vector<int> v;
    assert(std::is_sorted(v.cbegin(), v.cend()) && "an empty range is always sorted");
    v.push_back(42);
    assert(std::is_sorted(v.cbegin(), v.cend()) && "a range of size 1 is always sorted");
 
    int data[] = {3, 1, 4, 1, 5};
    assert(not std::is_sorted(std::begin(data), std::end(data)));
 
    std::sort(std::begin(data), std::end(data));
    assert(std::is_sorted(std::begin(data), std::end(data)));
    assert(not std::is_sorted(std::begin(data), std::end(data), std::greater<>{}));
}

[edit] See also

(C++11)
 finds the largest sorted subrange
(function template) [edit]
(C++20)
 checks whether a range is sorted into ascending order
(niebloid)[edit]
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