Definition: Rearrange a heap to maintain the heap property, that is, the key of the root node is more extreme (greater or less) than or equal to the keys of its children. If the root node's key is not more extreme, swap it with the most extreme child key, then recursively heapify that child's subtree. The child subtrees must be heaps to start.

See also binary heap, build-heap, heapsort.

Note: For an array implementation, heapify takes O(log2 n) or O(h) time under the comparison model, where n is the number of nodes and h is the height.

Author: PEB

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Entry modified 17 December 2004.
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Cite this as:
Paul E. Black, "heapify", in Dictionary of Algorithms and Data Structures [online], Vreda Pieterse and Paul E. Black, eds. 17 December 2004. (accessed TODAY) Available from: