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

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< cpp‎ | algorithm
(→‎Example: a comparator equivalent to std::less<int> is not a good idea IMO)
(Added LWG issue #3032 DR (part 2/2), and uses {{mark constexpr since c++20}}.)
 
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{{cpp/algorithm/navbar}}
 
{{cpp/algorithm/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
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{{dcl header | algorithm}}
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{{dcl header|algorithm}}
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{{dcl rev multi | num=1 | since1= | until1=c++20 |dcl1=
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{{dcl|num=1|notes={{mark constexpr since c++20}}|
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+
 
template< class RandomIt >
 
template< class RandomIt >
 
void make_heap( RandomIt first, RandomIt last );
 
void make_heap( RandomIt first, RandomIt last );
−
 
−
|dcl2=
 
−
template< class RandomIt >
 
−
constexpr void make_heap( RandomIt first, RandomIt last );
 
 
}}
 
}}
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{{dcl rev multi | num=2 | since1= | until1=c++20 |dcl1=
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{{dcl|num=2|notes={{mark constexpr since c++20}}|
−
 
+
−
template< class RandomIt, class Compare >
+
−
void make_heap( RandomIt first, RandomIt last,
+
−
                Compare comp );
+
−
 
+
−
|dcl2=
+
 
template< class RandomIt, class Compare >
 
template< class RandomIt, class Compare >
−
constexpr void make_heap( RandomIt first, RandomIt last,
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void make_heap( RandomIt first, RandomIt last, Compare comp );
−
                          Compare comp );
+
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
−
Constructs a ''max 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}}.
 +
 
 +
@1@ The constructed heap is with respect to {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
 +
@2@ The constructed heap is with respect to {{c|comp}}.
 +
 
 +
If any of the following conditions is satisfied, the behavior is undefined:
 +
{{rev begin}}
 +
{{rev|until=c++11|
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* The type of {{c|*first}} is not {{named req|Swappable}}.
 +
}}
 +
{{rev|since=c++11|
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* {{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===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par | first, last | the range of elements to make the heap from}}
+
{{par|first, last|the range to make the heap from}}
−
{{par cmp | comp | p1=RandomIt}}  
+
{{par cmp|comp|p1=RandomIt}}
 
{{par hreq}}
 
{{par hreq}}
−
{{par req named | RandomIt | RandomAccessIterator}}
+
{{par req named|RandomIt|RandomAccessIterator}}
−
{{par req named deref | RandomIt | MoveConstructible | MoveAssignable}}
+
{{par req named|Compare|Compare}}
 
{{par end}}
 
{{par end}}
−
 
−
===Return value===
 
−
(none)
 
  
 
===Complexity===
 
===Complexity===
−
At most {{c|3*std::distance(first, last)}} comparisons.
+
Given {{mathjax-or|\(\scriptsize N\)|N}} as {{c|std::distance(first, last)}}:
−
 
+
@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
−
|
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|
−
| code=
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|code=
−
#include <iostream>
+
 
#include <algorithm>
 
#include <algorithm>
 
#include <functional>
 
#include <functional>
 +
#include <iostream>
 +
#include <string_view>
 
#include <vector>
 
#include <vector>
  
−
int main()
+
void print(std::string_view text, const std::vector<int>& v = {})
 
{
 
{
−
     std::cout << "Max heap:\n";
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     std::cout << text << ": ";
−
 
+
     for (const auto& e : v)
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    std::vector<int> v { 3, 2, 4, 1, 5, 9 };
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        std::cout << e << ' ';
−
 
+
−
    std::cout << "initially, v: ";
+
−
     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);
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     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());
−
 
+
     print("after pop_heap, v", v);
−
     std::cout << "after pop_heap, v: ";
+
      
−
    for (auto i : v) std::cout << i << ' ';
+
−
     std::cout << '\n';
+
−
 
+
 
     auto top = v.back();
 
     auto top = v.back();
 
     v.pop_back();
 
     v.pop_back();
−
     std::cout << "former top element: " << top << '\n';
+
     print("former top element", {top});
−
 
+
     print("after removing the former top element, v", v);
−
     std::cout << "after removing the former top element, v: ";
+
      
−
    for (auto i : v) std::cout << i << ' ';
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     print("\nMin heap");
−
     std::cout << '\n' << '\n';
+
   
−
 
+
     std::vector<int> v1{3, 2, 4, 1, 5, 9};
−
     std::cout << "Min heap:\n";
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     print("initially, v1", v1);
−
 
+
      
−
     std::vector<int> v1 { 3, 2, 4, 1, 5, 9 };
+
−
 
+
−
     std::cout << "initially, v1: ";
+
−
    for (auto i : v1) std::cout << i << ' ';
+
−
     std::cout << '\n';
+
−
 
+
 
     std::make_heap(v1.begin(), v1.end(), std::greater<>{});
 
     std::make_heap(v1.begin(), v1.end(), std::greater<>{});
−
 
+
     print("after make_heap, v1", v1);
−
     std::cout << "after make_heap, v1: ";
+
      
−
    for (auto i : v1) std::cout << i << ' ';
+
−
     std::cout << '\n';
+
−
 
+
 
     std::pop_heap(v1.begin(), v1.end(), std::greater<>{});
 
     std::pop_heap(v1.begin(), v1.end(), std::greater<>{});
−
 
+
     print("after pop_heap, v1", v1);
−
     std::cout << "after pop_heap, v1: ";
+
      
−
    for (auto i : v1) std::cout << i << ' ';
+
−
     std::cout << '\n';
+
−
 
+
 
     auto top1 = v1.back();
 
     auto top1 = v1.back();
 
     v1.pop_back();
 
     v1.pop_back();
−
     std::cout << "former top element: " << top1 << '\n';
+
     print("former top element", {top1});
−
 
+
     print("after removing the former top element, v1", v1);
−
     std::cout << "after removing the former top element, v1: ";
+
−
    for (auto i : v1) std::cout << i << ' ';
+
−
    std::cout << '\n';
+
 
}
 
}
−
| output=
+
|output=
 
Max heap:
 
Max heap:
−
initially, v: 3 2 4 1 5 9  
+
initially, v: 3 2 4 1 5 9
−
after make_heap, v: 9 5 4 1 2 3  
+
after make_heap, v: 9 5 4 1 2 3
−
after pop_heap, v: 5 3 4 1 2 9  
+
after pop_heap, v: 5 3 4 1 2 9
 
former top element: 9
 
former top element: 9
−
after removing the former top element, v: 5 3 4 1 2  
+
after removing the former top element, v: 5 3 4 1 2
  
 
Min heap:
 
Min heap:
−
initially, v1: 3 2 4 1 5 9  
+
initially, v1: 3 2 4 1 5 9
−
after make_heap, v1: 1 2 4 3 5 9  
+
after make_heap, v1: 1 2 4 3 5 9
−
after pop_heap, v1: 2 3 4 9 5 1  
+
after pop_heap, v1: 2 3 4 9 5 1
 
former top element: 1
 
former top element: 1
 
after removing the former top element, v1: 2 3 4 9 5
 
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===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/algorithm/dsc sort_heap}}
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{{dsc inc|cpp/algorithm/dsc is_heap}}
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{{dsc inc | cpp/container/dsc priority_queue}}
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{{dsc inc|cpp/algorithm/dsc is_heap_until}}
−
{{dsc inc | cpp/utility/functional/dsc greater}}
+
{{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}}
 
{{dsc end}}
  
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[[de:cpp/algorithm/make heap]]
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
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[[es:cpp/algorithm/make heap]]
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[[fr:cpp/algorithm/make heap]]
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[[it:cpp/algorithm/make heap]]
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[[ja:cpp/algorithm/make heap]]
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[[pt:cpp/algorithm/make heap]]
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[[ru:cpp/algorithm/make heap]]
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[[zh:cpp/algorithm/make heap]]
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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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