Difference between revisions of "cpp/algorithm/ranges/pop heap"

Revision as of 01:23, 14 October 2024

Defined in header `<algorithm>`
Call signature
template< std::random_access_iterator I, std::sentinel_for<I> S, class Comp = ranges::less, class Proj = std::identity > requires std::sortable<I, Comp, Proj> constexpr I pop_heap( I first, S last, Comp comp = {}, Proj proj = {} );	(1)	(since C++20)
template< ranges::random_access_range R, class Comp = ranges::less, class Proj = std::identity > requires std::sortable<ranges::iterator_t<R>, Comp, Proj> constexpr ranges::borrowed_iterator_t<R> pop_heap( R&& r, Comp comp = {}, Proj proj = {} );	(2)	(since C++20)

Swaps the first element and the last element of the specified heap with respect to comp and proj and makes the subrange excluding the first position into a heap with respect to comp and proj. This has the effect of removing the first element from the specified heap.

1) The specified heap is [first, last).

2) The specified heap is r.

The function-like entities described on this page are niebloids, that is:

Explicit template argument lists cannot be specified when calling any of them.
None of them are visible to argument-dependent lookup.
When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

In practice, they may be implemented as function objects, or with special compiler extensions.

#include <algorithm>
#include <array>
#include <iostream>
#include <iterator>
#include <string_view>
 
template<class I = int*>
void print(std::string_view rem, I first = {}, I last = {},
           std::string_view term = "\n")
{
    for (std::cout << rem; first != last; ++first)
        std::cout << *first << ' ';
    std::cout << term;
}
 
int main()
{
    std::array v {3, 1, 4, 1, 5, 9, 2, 6, 5, 3};
    print("initially, v: ", v.cbegin(), v.cend());
 
    std::ranges::make_heap(v);
    print("make_heap, v: ", v.cbegin(), v.cend());
 
    print("convert heap into sorted array:");
    for (auto n {std::ssize(v)}; n >= 0; --n)
    {
        std::ranges::pop_heap(v.begin(), v.begin() + n);
        print("[ ", v.cbegin(), v.cbegin() + n, "]  ");
        print("[ ", v.cbegin() + n, v.cend(), "]\n");
    }
}

Output:

initially, v: 3 1 4 1 5 9 2 6 5 3
make_heap, v: 9 6 4 5 5 3 2 1 1 3
convert heap into sorted array:
[ 6 5 4 3 5 3 2 1 1 9 ]  [ ]
[ 5 5 4 3 1 3 2 1 6 ]  [ 9 ]
[ 5 3 4 1 1 3 2 5 ]  [ 6 9 ]
[ 4 3 3 1 1 2 5 ]  [ 5 6 9 ]
[ 3 2 3 1 1 4 ]  [ 5 5 6 9 ]
[ 3 2 1 1 3 ]  [ 4 5 5 6 9 ]
[ 2 1 1 3 ]  [ 3 4 5 5 6 9 ]
[ 1 1 2 ]  [ 3 3 4 5 5 6 9 ]
[ 1 1 ]  [ 2 3 3 4 5 5 6 9 ]
[ 1 ]  [ 1 2 3 3 4 5 5 6 9 ]
[ ]  [ 1 1 2 3 3 4 5 5 6 9 ]

@@ Line 7: / Line 7: @@
 template< std::random_access_iterator I, std::sentinel_for<I> S,
            class Comp = ranges::less, class Proj = std::identity >
-requires std::sortable<I, Comp, Proj>
+    requires std::sortable<I, Comp, Proj>
-constexpr I
+constexpr I pop_heap( I first, S last, Comp comp = {}, Proj proj = {} );
-    pop_heap( I first, S last, Comp comp = {}, Proj proj = {} );
 }}
 {{dcl|num=2|since=c++20|1=
-template< ranges::random_access_range R, class Comp = ranges::less,
+template< ranges::random_access_range R,
-          class Proj = std::identity >
+          class Comp = ranges::less, class Proj = std::identity >
-requires std::sortable<ranges::iterator_t<R>, Comp, Proj>
+    requires std::sortable<ranges::iterator_t<R>, Comp, Proj>
 constexpr ranges::borrowed_iterator_t<R>
      pop_heap( R&& r, Comp comp = {}, Proj proj = {} );
@@ Line 20: / Line 19: @@
 {{dcl end}}
-Swaps the value in the position {{c|first}} and the value in the position {{c|last - 1}} and makes the subrange {{range|first|last - 1}} into a {{enwiki|Binary heap|max heap}}. This has the effect of removing the first element from the heap defined by the range {{range|first|last}}.
+Swaps the first element and the last element of the specified [[cpp/algorithm#Heap operations|heap]] with respect to {{c|comp}} and {{c|proj}} and makes the subrange excluding the first position into a heap with respect to {{c|comp}} and {{c|proj}}. This has the effect of removing the first element from the specified heap.
-@1@ Elements are compared using the given binary comparison function {{c|comp}} and projection object {{c|proj}}.
+@1@ The specified heap is {{range|first|last}}.
-@2@ Same as {{v|1}}, but uses {{c|r}} as the range, as if using {{c|ranges::begin(r)}} as {{c|first}} and {{c|ranges::end(r)}} as {{c|last}}.
+@2@ The specified heap is {{c|r}}.
 {{cpp/ranges/niebloid}}
@@ Line 30: / Line 29: @@
 ===Parameters===
 {{par begin}}
-{{par|first, last|the range of elements defining the valid nonempty heap to modify}}
+{{par|first, last|the iterator and sentinel designating the range of elements to modify}}
-{{par|r|the range of elements defining the valid nonempty heap to modify}}
+{{par|r|the range of elements to modify}}
-{{par|pred|predicate to apply to the projected elements}}
+{{par|comp|comparator to apply to the projected elements}}
 {{par|proj|projection to apply to the elements}}
 {{par end}}
 ===Return value===
-An iterator equal to {{c|last}}.
+@1@ {{c|last}}
+@2@ {{c|ranges::end(r)}}
 ===Complexity===
-Given {{c|1= N = ranges::distance(first, last)}}, at most {{mathjax-or|\(\scriptsize 2\log{(N)}\)|2log(N)}} comparisons and {{mathjax-or|\(\scriptsize 4\log{(N)}\)|4log(N)}} projections.
+At most {{mathjax-or|\(\scriptsize 2\log{(N)}\)|2log(N)}} applications of {{c|comp}} and {{mathjax-or|\(\scriptsize 4\log{(N)}\)|4log(N)}} applications of {{c|proj}}, where {{mathjax-or|\(\scriptsize N \)|N}} is:
+@1@ {{c|ranges::distance(first, last)}}
-===Notes===
+@2@ {{c|ranges::distance(r)}}
-{{cpp/algorithm/ranges/notes heap}}
 ===Example===
@@ Line 67: / Line 66: @@
      std::array v {3, 1, 4, 1, 5, 9, 2, 6, 5, 3};
      print("initially, v: ", v.cbegin(), v.cend());
      std::ranges::make_heap(v);
      print("make_heap, v: ", v.cbegin(), v.cend());
      print("convert heap into sorted array:");
      for (auto n {std::ssize(v)}; n >= 0; --n)

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Feature test macros (C++20)
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Concepts library (C++20)
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Ranges library (C++20)
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Filesystem library (C++17)
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Execution support library (C++26)
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External libraries

first, last	-	the iterator and sentinel designating the range of elements to modify
r	-	the range of elements to modify
comp	-	comparator to apply to the projected elements
proj	-	projection to apply to the elements

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

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Difference between revisions of "cpp/algorithm/ranges/pop heap"

Revision as of 01:23, 14 October 2024

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