push_heap push_heap Category: algorithms Component type: function Prototype Push_heap is an overloaded name; there are actually two push_heap functions. template <class RandomAccessIterator> void push_heap(RandomAccessIterator first, RandomAccessIterator last); template <class RandomAccessIterator, class StrictWeakOrdering> void push_heap(RandomAccessIterator first, RandomAccessIterator last, StrictWeakOrdering comp); Description Push_heap adds an element to a heap [1]. It is assumed that [first, last - 1) is already a heap; the element to be added to the heap is *(last - 1). The two versions of push_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. The postcondition for the first version is that is_heap(first, last) is true, and the postcondition for the second version is that is_heap(first, last, comp) is true. Definition Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h. Requirements on types 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. Preconditions For the first version: [first, last) is a valid range. [first, last - 1) is a valid range. That is, [first, last) is nonempty. [first, last - 1) is a heap. That is, is_heap(first, last - 1) is true. For the second version: [first, last) is a valid range. [first, last - 1) is a valid range. That is, [first, last) is nonempty. [first, last) is a heap. That is, is_heap(first, last - 1, comp) is true. Complexity Logarithmic. At most log(last - first) comparisons. Example int main() { int A[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }; make_heap(A, A + 9); cout << "[A, A + 9) = "; copy(A, A + 9, ostream_iterator<int>(cout, " ")); push_heap(A, A + 10); cout << endl << "[A, A + 10) = "; copy(A, A + 10, ostream_iterator<int>(cout, " ")); cout << endl; } The output is [A, A + 9) = 8 7 6 3 4 5 2 1 0 [A, A + 10) = 9 8 6 3 7 5 2 1 0 4 Notes [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 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. See also make_heap, pop_heap, sort_heap, is_heap, sort Copyright © 1999 Silicon Graphics, Inc. All Rights Reserved. TrademarkInformation