Книга: Standard Template Library Programmer



Category: algorithms

Component type: function


Is_heap is an overloaded name; there are actually two is_heap functions.

template <class RandomAccessIterator>
bool is_heap(RandomAccessIterator first, RandomAccessIterator last);
template <class RandomAccessIterator, class StrictWeakOrdering>
inline bool is_heap(RandomAccessIterator first, RandomAccessIterator last, StrictWeakOrdering comp)


Is_heap returns true if the range [first, last) is a heap [1], and false otherwise. The two versions 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.


Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h. This function is an SGI extension; it is not part of the C++ standard.

Requirements on types

For the first version:

• RandomAccessIterator is a model of Random Access Iterator.

• 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.

• 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. Zero comparisons if [first, last) is an empty range, otherwise at most (last – first) – 1 comparisons.


int A[] = {1, 2, 3, 4, 5, 6, 7};
const int N = sizeof(A) / sizeof(int);
assert(!is_heap(A, A+N));
make_heap(A, A+N);
assert(is_heap(A, A+N));


[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, push_heap, pop_heap, sort_heap

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