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

Latest revision as of 19:22, 8 April 2024

Defined in header `<algorithm>`
template< class RandomIt > bool is_heap( RandomIt first, RandomIt last );	(1)	(since C++11) (constexpr since C++20)
template< class ExecutionPolicy, class RandomIt > bool is_heap( ExecutionPolicy&& policy, RandomIt first, RandomIt last );	(2)	(since C++17)
template< class RandomIt, class Compare > bool is_heap( RandomIt first, RandomIt last, Compare comp );	(3)	(since C++11) (constexpr since C++20)
template< class ExecutionPolicy, class RandomIt, class Compare > bool is_heap( ExecutionPolicy&& policy, RandomIt first, RandomIt last, Compare comp );	(4)	(since C++17)

Checks whether [first, last) is a heap.

1) The heap property to be checked is with respect to operator<(until C++20)std::less{}(since C++20).

3) The heap property to be checked is 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)

first, last	-	the range to be checked
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 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 RandomIt can be dereferenced and then implicitly converted to both of them.
Type requirements
- `RandomIt` must meet the requirements of LegacyRandomAccessIterator.
- `Compare` must meet the requirements of Compare.

[edit] Return value

true if the range is a heap with respect to the corresponding comparator, false otherwise.

[edit] Complexity

Given $\scriptsize N$ $N$ 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 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] Example

Run this code

#include <algorithm>
#include <bit>
#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v{3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 7, 9};
 
    std::cout << "initially, v:\n";
    for (const auto& i : v)
        std::cout << i << ' ';
    std::cout << '\n';
 
    if (!std::is_heap(v.begin(), v.end()))
    {
        std::cout << "making heap...\n";
        std::make_heap(v.begin(), v.end());
    }
 
    std::cout << "after make_heap, v:\n";
    for (auto t{1U}; const auto& i : v)
        std::cout << i << (std::has_single_bit(++t) ? " | " : " ");
    std::cout << '\n';
}

Output:

initially, v:
3 1 4 1 5 9 2 6 5 3 5 8 9 7 9
making heap...
after make_heap, v:
9 | 6 9 | 5 5 9 7 | 1 1 3 5 8 3 4 2 |

[edit] See also

is_heap_until (C++11)	finds the largest subrange that is a max heap (function template) [edit]
make_heap	creates a max heap out of a range of elements (function template) [edit]
push_heap	adds an element to a max heap (function template) [edit]
pop_heap	removes the largest element from a max heap (function template) [edit]
sort_heap	turns a max heap into a range of elements sorted in ascending order (function template) [edit]
ranges::is_heap (C++20)	checks if the given range is a max heap (niebloid)[edit]

@@ Line 1: / Line 1: @@
 {{cpp/title|is_heap}}
-{{cpp/algorithm/sidebar}}
+{{cpp/algorithm/navbar}}
-{{ddcl list begin}}
+{{dcl begin}}
-{{ddcl list header | algorithm}}
+{{dcl header|algorithm}}
-{{ddcl list item | num=1 |
+{{dcl|num=1|since=c++11|notes={{mark constexpr since c++20}}|
-template< class RandomAccessIterator >
+template< class RandomIt >
-bool is_heap( RandomAccessIterator first, RandomAccessIterator last );
+bool is_heap( RandomIt first, RandomIt last );
 }}
-{{ddcl list item | num=2 |
+{{dcl|num=2|since=c++17|
-template< class RandomAccessIterator, class Compare >
+template< class ExecutionPolicy, class RandomIt >
-bool is_heap( RandomAccessIterator first, RandomAccessIterator last, Compare comp );
+bool is_heap( ExecutionPolicy&& policy,
+              RandomIt first, RandomIt last );
 }}
-{{ddcl list end}}
+{{dcl|num=3|since=c++11|notes={{mark constexpr since c++20}}|
+template< class RandomIt, class Compare >
+bool is_heap( RandomIt first, RandomIt last, Compare comp );
+}}
+{{dcl|num=4|since=c++17|
+template< class ExecutionPolicy, class RandomIt, class Compare >
+bool is_heap( ExecutionPolicy&& policy,
+              RandomIt first, RandomIt last, Compare comp );
+}}
+{{dcl end}}
-Checks if the elements in range {{tt|[first, last)}} is a ''heap''. The first version of the function uses {{cpp|operator<}} to compare the elements, the second uses the given comparison function {{tt|comp}}.
+Checks whether {{range|first|last}} is a {{rlp|/#Heap operations|heap}}.
+@1@ The heap property to be checked is with respect to {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
+@3@ The heap property to be checked is with respect to {{c|comp}}.
+@2,4@ Same as {{v|1,3}}, but executed according to {{c|policy}}.
+@@ {{cpp/algorithm/parallel overload precondition|plural=yes}}
-<!-- ======== -->
 ===Parameters===
-{{param list begin}}
+{{par begin}}
-{{param list item | first, last | the range of elements to examine}}
+{{par|first, last|the range to be checked}}
-{{param list cmp | comp | p1=RandomAccessIterator}}
+{{par exec pol}}
-{{param list end}}
+{{par cmp|comp|p1=RandomIt}}
+{{par hreq}}
+{{par req named|RandomIt|RandomAccessIterator}}
+{{par req named|Compare|Compare}}
+{{par end}}
-<!-- ======== -->
 ===Return value===
-{{cpp|true}} if the range is ''heap'', {{cpp|false}} otherwise.
+{{c|true}} if the range is a heap with respect to the corresponding comparator, {{c|false}} otherwise.
-<!-- ======== -->
 ===Complexity===
+Given {{mathjax-or|\(\scriptsize N\)|N}} as {{c|std::distance(first, last)}}:
-linear in the distance between {{tt|first}} and {{tt|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 comparison function {{c|comp}}.
+===Exceptions===
+{{cpp/algorithm/parallel exceptions reporting behavior|singular=no}}
-<!-- ======== -->
 ===Example===
-{{example cpp
+{{example
- |
+|code=
- | code=
+#include <algorithm>
- | output=
+#include <bit>
+#include <iostream>
+#include <vector>
+int main()
+{
+    std::vector<int> v{3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 7, 9};
+    std::cout << "initially, v:\n";
+    for (const auto& i : v)
+        std::cout << i << ' ';
+    std::cout << '\n';
+    if (!std::is_heap(v.begin(), v.end()))
+    {
+        std::cout << "making heap...\n";
+        std::make_heap(v.begin(), v.end());
+    }
+    std::cout << "after make_heap, v:\n";
+    for (auto t{1U}; const auto& i : v)
+        std::cout << i << (std::has_single_bit(++t) ? " {{!}} " : " ");
+    std::cout << '\n';
+}
+|output=
+initially, v:
+1 4 1 5 9 2 6 5 3 5 8 9 7 9
+making heap...
+after make_heap, v:
+{{!}} 6 9 {{!}} 5 5 9 7 {{!}} 1 1 3 5 8 3 4 2 {{!}}
 }}
-<!-- ======== -->
-{{notes}}
-{{cpp/algorithm/notes heap}}
-<!-- ======== -->
 ===See also===
-{{dcl list begin}}
+{{dsc begin}}
-{{dcl list template | cpp/algorithm/dcl list is_heap_until}}
+{{dsc inc|cpp/algorithm/dsc is_heap_until}}
-{{dcl list end}}
+{{dsc inc|cpp/algorithm/dsc make_heap}}
+{{dsc inc|cpp/algorithm/dsc push_heap}}
+{{dsc inc|cpp/algorithm/dsc pop_heap}}
+{{dsc inc|cpp/algorithm/dsc sort_heap}}
+{{dsc inc|cpp/algorithm/ranges/dsc is_heap}}
+{{dsc end}}
+{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

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

Latest revision as of 19:22, 8 April 2024

Contents

[edit] Parameters

[edit] Return value

[edit] Complexity

[edit] Exceptions

[edit] Example

[edit] See also

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