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

From cppreference.com
< cpp‎ | algorithm
(added example)
(Added LWG issue #3032 DR (part 2/2), and uses {{mark constexpr since c++20}}.)
 
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{{cpp/title|make_heap}}
 
{{cpp/title|make_heap}}
−
{{cpp/algorithm/sidebar}}
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{{cpp/algorithm/navbar}}
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{{ddcl list begin}}
+
{{dcl begin}}
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{{ddcl list header | algorithm}}
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{{dcl header|algorithm}}
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{{ddcl list item | num=1 |
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{{dcl|num=1|notes={{mark constexpr since c++20}}|
−
template< class RandomAccessIterator >
+
template< class RandomIt >
−
void make_heap( RandomAccessIterator first, RandomAccessIterator last );
+
void make_heap( RandomIt first, RandomIt last );
 
}}
 
}}
−
{{ddcl list item | num=2 |
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{{dcl|num=2|notes={{mark constexpr since c++20}}|
−
template< class RandomAccessIterator, class Compare >
+
template< class RandomIt, class Compare >
−
void make_heap( RandomAccessIterator first, RandomAccessIterator last,
+
void make_heap( RandomIt first, RandomIt last, Compare comp );
−
                Compare comp );
+
 
}}
 
}}
−
{{ddcl list end}}
+
{{dcl end}}
  
−
Constructs a ''heap'' in the range {{tt|[first, last)}}. The first version of the function uses {{c|operator<}} to compare the elements, the second uses the given comparison function {{tt|comp}}.
+
Constructs a {{rlp|/#Heap operations|heap}} in the range {{range|first|last}}.
  
−
===Parameters===
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@1@ The constructed heap is with respect to {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
−
{{param list begin}}
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@2@ The constructed heap is with respect to {{c|comp}}.
−
{{param list item | first, last | the range of elements to make the heap from}}
+
−
{{param list cmp | comp | p1=RandomAccessIterator}}  
+
−
{{param list end}}
+
  
−
===Return value===
+
If any of the following conditions is satisfied, the behavior is undefined:
−
(none)
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{{rev begin}}
 +
{{rev|until=c++11|
 +
* The type of {{c|*first}} is not {{named req|Swappable}}.
 +
}}
 +
{{rev|since=c++11|
 +
* {{tt|RandomIt}} is not {{named req|ValueSwappable}}.
 +
* The type of {{c|*first}} is not {{named req|MoveConstructible}}.
 +
* The type of {{c|*first}} is not {{named req|MoveAssignable}}.
 +
}}
 +
{{rev end}}
 +
 
 +
===Parameters===
 +
{{par begin}}
 +
{{par|first, last|the range to make the heap from}}
 +
{{par cmp|comp|p1=RandomIt}}
 +
{{par hreq}}
 +
{{par req named|RandomIt|RandomAccessIterator}}
 +
{{par req named|Compare|Compare}}
 +
{{par end}}
  
 
===Complexity===
 
===Complexity===
−
At most {{c|3*std::distance(first, last)}} comparisons.
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Given {{mathjax-or|\(\scriptsize N\)|N}} as {{c|std::distance(first, last)}}:
−
 
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@1@ At most {{mathjax-or|\(\scriptsize 3N\)|3N}} comparisons using {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
−
===Notes===
+
@2@ At most {{mathjax-or|\(\scriptsize 3N\)|3N}} applications of the comparison function {{c|comp}}.
−
{{cpp/algorithm/notes heap}}
+
  
 
===Example===
 
===Example===
 
{{example
 
{{example
−
|
+
|
−
| code=
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|code=
−
#include <iostream>
+
 
#include <algorithm>
 
#include <algorithm>
 +
#include <functional>
 +
#include <iostream>
 +
#include <string_view>
 +
#include <vector>
  
−
int main()
+
void print(std::string_view text, const std::vector<int>& v = {})
 
{
 
{
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    std::vector<int> v { 3, 1, 4, 1, 5, 9 };
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     std::cout << text << ": ";
−
 
+
     for (const auto& e : v)
−
     std::cout << "initially, v: ";
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        std::cout << e << ' ';
−
     for (auto i : v) std::cout << i << ' ';
+
 
     std::cout << '\n';
 
     std::cout << '\n';
 +
}
  
 +
int main()
 +
{
 +
    print("Max heap");
 +
   
 +
    std::vector<int> v{3, 2, 4, 1, 5, 9};
 +
    print("initially, v", v);
 +
   
 
     std::make_heap(v.begin(), v.end());
 
     std::make_heap(v.begin(), v.end());
−
 
+
     print("after make_heap, v", v);
−
     std::cout << "after make_heap, v: ";
+
      
−
    for (auto i : v) std::cout << i << ' ';
+
−
     std::cout << '\n';
+
−
 
+
 
     std::pop_heap(v.begin(), v.end());
 
     std::pop_heap(v.begin(), v.end());
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     auto largest = v.back();
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    print("after pop_heap, v", v);
 +
   
 +
     auto top = v.back();
 
     v.pop_back();
 
     v.pop_back();
−
     std::cout << "largest element: " << largest << '\n';
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     print("former top element", {top});
−
 
+
     print("after removing the former top element, v", v);
−
     std::cout << "after removing the largest element, v: ";
+
      
−
     for (auto i : v) std::cout << i << ' ';
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    print("\nMin heap");
−
     std::cout << '\n';
+
   
 +
    std::vector<int> v1{3, 2, 4, 1, 5, 9};
 +
    print("initially, v1", v1);
 +
   
 +
    std::make_heap(v1.begin(), v1.end(), std::greater<>{});
 +
    print("after make_heap, v1", v1);
 +
   
 +
     std::pop_heap(v1.begin(), v1.end(), std::greater<>{});
 +
    print("after pop_heap, v1", v1);
 +
   
 +
    auto top1 = v1.back();
 +
    v1.pop_back();
 +
    print("former top element", {top1});
 +
    print("after removing the former top element, v1", v1);
 
}
 
}
−
| output=
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|output=
−
initially, v: 3 1 4 1 5 9  
+
Max heap:
−
after make_heap, v: 9 5 4 1 1 3  
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initially, v: 3 2 4 1 5 9
−
largest element: 9
+
after make_heap, v: 9 5 4 1 2 3
−
after removing the largest element, v: 5 3 4 1 1  
+
after pop_heap, v: 5 3 4 1 2 9
 +
former top element: 9
 +
after removing the former top element, v: 5 3 4 1 2
 +
 
 +
Min heap:
 +
initially, v1: 3 2 4 1 5 9
 +
after make_heap, v1: 1 2 4 3 5 9
 +
after pop_heap, v1: 2 3 4 9 5 1
 +
former top element: 1
 +
after removing the former top element, v1: 2 3 4 9 5
 
}}
 
}}
 +
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{dr list item|wg=lwg|dr=3032|std=C++98|before=the elements of {{range|first|last}} was not required to be swappable|after=required}}
 +
{{dr list end}}
  
 
===See also===
 
===See also===
−
{{dcl list begin}}
+
{{dsc begin}}
−
{{dcl list template | cpp/algorithm/dcl list sort_heap}}
+
{{dsc inc|cpp/algorithm/dsc is_heap}}
−
{{dcl list end}}
+
{{dsc inc|cpp/algorithm/dsc is_heap_until}}
 +
{{dsc inc|cpp/algorithm/dsc push_heap}}
 +
{{dsc inc|cpp/algorithm/dsc pop_heap}}
 +
{{dsc inc|cpp/algorithm/dsc sort_heap}}
 +
{{dsc inc|cpp/container/dsc priority_queue}}
 +
{{dsc inc|cpp/algorithm/ranges/dsc make_heap}}
 +
{{dsc end}}
  
−
[[ru:cpp/algorithm/make heap]]
+
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Latest revision as of 18:24, 8 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
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
make_heap
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 RandomIt >
void make_heap( RandomIt first, RandomIt last );
 (1) (constexpr since C++20)
template< class RandomIt, class Compare >
void make_heap( RandomIt first, RandomIt last, Compare comp );
 (2) (constexpr since C++20)

Constructs a heap in the range [first, last).

1) The constructed heap is with respect to operator<(until C++20)std::less{}(since C++20).
2) The constructed heap is with respect to comp.

If any of the following conditions is satisfied, the behavior is undefined:

(until C++11)
(since C++11)

Contents

[edit] Parameters

first, last - the range to make the heap from
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] Complexity

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

1) At most 3N comparisons using operator<(until C++20)std::less{}(since C++20).
2) At most 3N applications of the comparison function comp.

[edit] Example

Run this code
#include <algorithm>
#include <functional>
#include <iostream>
#include <string_view>
#include <vector>
 
void print(std::string_view text, const std::vector<int>& v = {})
{
    std::cout << text << ": ";
    for (const auto& e : v)
        std::cout << e << ' ';
    std::cout << '\n';
}
 
int main()
{
    print("Max heap");
 
    std::vector<int> v{3, 2, 4, 1, 5, 9};
    print("initially, v", v);
 
    std::make_heap(v.begin(), v.end());
    print("after make_heap, v", v);
 
    std::pop_heap(v.begin(), v.end());
    print("after pop_heap, v", v);
 
    auto top = v.back();
    v.pop_back();
    print("former top element", {top});
    print("after removing the former top element, v", v);
 
    print("\nMin heap");
 
    std::vector<int> v1{3, 2, 4, 1, 5, 9};
    print("initially, v1", v1);
 
    std::make_heap(v1.begin(), v1.end(), std::greater<>{});
    print("after make_heap, v1", v1);
 
    std::pop_heap(v1.begin(), v1.end(), std::greater<>{});
    print("after pop_heap, v1", v1);
 
    auto top1 = v1.back();
    v1.pop_back();
    print("former top element", {top1});
    print("after removing the former top element, v1", v1);
}

Output: 

Max heap:
initially, v: 3 2 4 1 5 9
after make_heap, v: 9 5 4 1 2 3
after pop_heap, v: 5 3 4 1 2 9
former top element: 9
after removing the former top element, v: 5 3 4 1 2
 
Min heap:
initially, v1: 3 2 4 1 5 9
after make_heap, v1: 1 2 4 3 5 9
after pop_heap, v1: 2 3 4 9 5 1
former top element: 1
after removing the former top element, v1: 2 3 4 9 5

[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 3032 C++98 the elements of [first, last) was not required to be swappable required

[edit] See also

(C++11)
 checks if the given range is a max heap
(function template) [edit]
(C++11)
 finds the largest subrange that is a max heap
(function template) [edit]
adds an element to a max heap
(function template) [edit]
removes the largest element from a max heap
(function template) [edit]
turns a max heap into a range of elements sorted in ascending order
(function template) [edit]
adapts a container to provide priority queue
(class template) [edit]
(C++20)
 creates a max heap out of a range of elements
(niebloid)[edit]
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