std::make_heap

 

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C library
qsort	bsearch

 

Defined in header <algorithm>
template< class RandomAccessIterator > void make_heap( RandomAccessIterator first, RandomAccessIterator last );	(1)
template< class RandomAccessIterator, class Compare > void make_heap( RandomAccessIterator first, RandomAccessIterator last,                 Compare comp );	(2)

Constructs a heap in the range [first, last). The first version of the function uses operator< to compare the elements, the second uses the given comparison function comp.

Parameters

first, last	-	the range of elements to make the heap from
comp	-	comparison function 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); The signature does not need to have const &, but the function must not modify the objects passed to it. The types  Type1 and  Type2 must be such that an object of type RandomAccessIterator can be dereferenced and then implicitly converted to both of them. ​

Return value

(none)

Complexity

At most 3*std::distance(first, last) comparisons.

Notes

A heap is a range of elements [f,l) that has the following properties:

• *f is the largest element in the range
• a new element can be added using std::push_heap()
• the first element can be removed using std::pop_heap()

The actual arrangement of the elements is implementation defined.

Example

#include <iostream>
#include <algorithm>
 
int main()
{
    std::vector<int> v { 3, 1, 4, 1, 5, 9 };
 
    std::cout << "initially, v: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
 
    std::make_heap(v.begin(), v.end());
 
    std::cout << "after make_heap, v: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
 
    std::pop_heap(v.begin(), v.end());
    auto largest = v.back();
    v.pop_back();
    std::cout << "largest element: " << largest << '\n';
 
    std::cout << "after removing the largest element, v: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
}

Output:

initially, v: 3 1 4 1 5 9 
after make_heap, v: 9 5 4 1 1 3 
largest element: 9
after removing the largest element, v: 5 3 4 1 1

See also

sort_heap	turns a heap into a sorted range of elements (function template)