Книга: Standard Template Library Programmer

make_heap

make_heap

Category: algorithms

Component type: function

Make_heap is an overloaded name; there are actually two make_heap functions.

template <class RandomAccessIterator>
void make_heap(RandomAccessIterator first, RandomAccessIterator last);
template <class RandomAccessIterator, class StrictWeakOrdering>
void make_heap(RandomAccessIterator first, RandomAccessIterator last, StrictWeakOrdering comp);

Make_heap turns the range [first, last) into a heap [1].

The two versions of make_heap differ in how they define whether one element is less than another. The first version compares objects using operator<, and the second compares objects using a function object comp. In the first version the postcondition is that is_heap(first, last) is true, and in the second version the postcondition is that is_heap(first, last, comp) is true.

Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.

For the first version:

• RandomAccessIterator is a model of Random Access Iterator.

• RandomAccessIterator is mutable.

• RandomAccessIterator's value type is a model of LessThan Comparable.

• The ordering on objects of RandomAccessIterator's value type is a strict weak ordering, as defined in the LessThan Comparable requirements.

For the second version:

• RandomAccessIterator is a model of Random Access Iterator.

• RandomAccessIterator is mutable.

• StrictWeakOrdering is a model of Strict Weak Ordering.

• RandomAccessIterator's value type is convertible to StrictWeakOrdering's argument type.

• [first, last) is a valid range.

Linear. At most 3*(last – first) comparisons.

int main() {
 int A[] = {1, 4, 2, 8, 5, 7};
 const int N = sizeof(A) / sizeof(int);
 make_heap(A, A+N);
 copy(A, A+N, ostream_iterator<int>(cout, " "));
 cout << endl;
 sort_heap (A, A+N);
 copy(A, A+N, ostream_iterator <int>(cout, " "));
 cout << endl;
}

[1] A heap is a particular way of ordering the elements in a range of Random Access Iterators [f, l). The reason heaps are useful (especially for sorting, or as priority queues) is that they satisfy two important properties. First, *f is the largest element in the heap. Second, it is possible to add an element to a heap (using push_heap), or to remove *f, in logarithmic time. Internally, a heap is simply a tree represented as a sequential range. The tree is constructed so that that each node is less than or equal to its parent node.

push_heap , pop_heap , sort_heap , sort , is_heap

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