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An area of memory used for dynamic memory allocation where blocks of memory are allocated and freed in an arbitrary order and the pattern of allocation and size of blocks is not known until run time. Typically, a program has one heap which it may use for several different purposes.

Heap is required by languages in which functions can return arbitrary data structures or functions with free variables (see closure). In C functions malloc and free provide access to the heap.

Contrast stack. See also dangling pointer.


A data structure with its elements partially ordered (sorted) such that finding either the minimum or the maximum (but not both) of the elements is computationally inexpensive (independent of the number of elements), while both adding a new item and finding each subsequent smallest/largest element can be done in O(log n) time, where n is the number of elements.

Formally, a heap is a binary tree with a key in each node, such that all the leaves of the tree are on two adjacent levels; all leaves on the lowest level occur to the left and all levels, except possibly the lowest, are filled; and the key in the root is at least as large as the keys in its children (if any), and the left and right subtrees (if they exist) are again heaps.

Note that the last condition assumes that the goal is finding the minimum quickly.

Heaps are often implemented as one-dimensional arrays. Still assuming that the goal is finding the minimum quickly the invariant is

heap[i] <= heap[2*i] and heap[i] <= heap[2*i+1] for all i,

where heap[i] denotes the i-th element, heap[1] being the first. Heaps can be used to implement priority queues or in sort algorithms.


In programming, it refers to a common pool of memory that is available to the program. The management of the heap is either done by the applications themselves, allocating and deallocating memory as required, or by the operating system or other system program.
References in periodicals archive ?
Scotland languish at the bottom of the heap after another disappointing display yesterday in the Four Nations at Bainfield, Edinburgh.
Joining the XAL at the bottom of the heap are yesterday's leader, the PHLX Gold and Silver Index , the Morgan Stanley Cyclical Index and the AMEX Networking Index .
Those at the bottom of the heap are left to their own devices, and it has always been the same.
Malcolm Leatherland, weighbridge clerk at the scrapyard, said: "A battery on a car at the bottom of the heap shorted and started the fire.
Many recipients are at the bottom of the heap, wasted by booze, heroin or crack cocaine, and plagued by mental disease or physical maladies, according to opponents of the law.
She said: "The picture at the bottom of the heap is pitiful, absolutely pitiful.
They're the serfs at the bottom of the heap being milked for every groat they've got.
Languishing at the bottom of the heap is deeply-troubled Fiat, while in 32nd place Peugeot, despite the hugely fashionable 206, has clearly been held back by indifferent assembly, ageing design and soft engines.
He insists it is easier trying to stay at the top of the pile than it is when you are propping up the rest at the bottom of the heap.
Don Hildred, spokesman for Stratford-upon-Avon Ramblers Association in Warwickshire, said: ``Footpaths have been at the bottom of the heap in terms of council priorities for a long time.
At the bottom of the heap were food vendors (4 percent) and sports merchandise vendors (2 percent).
1 status while sports like baseball and badminton wound up at the bottom of the heap.