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Struct std.container.binaryheap.BinaryHeap

Implements a binary heap container on top of a given random-access range type (usually T[]) or a random-access container type (usually Array!T). The documentation of BinaryHeap will refer to the underlying range or container as the store of the heap.

The binary heap induces structure over the underlying store such that accessing the largest element (by using the front property) is a Ο(1) operation and extracting it (by using the removeFront() method) is done fast in Ο(log n) time.

If less is the less-than operator, which is the default option, then BinaryHeap defines a so-called max-heap that optimizes extraction of the largest elements. To define a min-heap, instantiate BinaryHeap with "a > b" as its predicate.

Simply extracting elements from a BinaryHeap container is tantamount to lazily fetching elements of Store in descending order. Extracting elements from the BinaryHeap to completion leaves the underlying store sorted in ascending order but, again, yields elements in descending order.

If Store is a range, the BinaryHeap cannot grow beyond the size of that range. If Store is a container that supports insertBack, the BinaryHeap may grow by adding elements to the container.

Constructors

Name Description
this Converts the store s into a heap. If initialSize is specified, only the first initialSize elements in s are transformed into a heap, after which the heap can grow up to r.length (if Store is a range) or indefinitely (if Store is a container with insertBack). Performs Ο(min(r.length, initialSize)) evaluations of less.

Properties

Name Type Description
capacity [get] size_t Returns the capacity of the heap, which is the length of the underlying store (if the store is a range) or the capacity of the underlying store (if the store is a container).
dup [get] BinaryHeap Returns a duplicate of the heap. The underlying store must also support a dup method.
empty [get] bool Returns true if the heap is empty, false otherwise.
front [get] ElementType!Store Returns a copy of the front of the heap, which is the largest element according to less.
length [get] size_t Returns the length of the heap.

Methods

Name Description
acquire Takes ownership of a store. After this, manipulating s may make the heap work incorrectly.
assume Takes ownership of a store assuming it already was organized as a heap.
clear Clears the heap by detaching it from the underlying store.
conditionalInsert If the heap has room to grow, inserts value into the store and returns true. Otherwise, if less(value, front), calls replaceFront(value) and returns again true. Otherwise, leaves the heap unaffected and returns false. This method is useful in scenarios where the smallest k elements of a set of candidates must be collected.
insert Inserts value into the store. If the underlying store is a range and length == capacity, throws an exception.
release Clears the heap. Returns the portion of the store from 0 up to length, which satisfies the heap property.
removeAny Removes the largest element from the heap and returns a copy of it. The element still resides in the heap's store. For performance reasons you may want to use removeFront with heaps of objects that are expensive to copy.
removeFront Removes the largest element from the heap.
replaceFront Replaces the largest element in the store with value.

Aliases

Name Description
popFront Removes the largest element from the heap.

Example

Example from "Introduction to Algorithms" Cormen et al, p 146 

import std.algorithm : equal;
int[] a = [ 4, 1, 3, 2, 16, 9, 10, 14, 8, 7 ];
auto h = heapify(a);
// largest element
assert(h.front == 16);
// a has the heap property
assert(equal(a, [ 16, 14, 10, 8, 7, 9, 3, 2, 4, 1 ]));

Example

BinaryHeap implements the standard input range interface, allowing

lazy iteration of the underlying range in descending order. 

import std.algorithm : equal;
import std.range : take;
int[] a = [4, 1, 3, 2, 16, 9, 10, 14, 8, 7];
auto top5 = heapify(a).take(5);
assert(top5.equal([16, 14, 10, 9, 8]));

Authors

Steven Schveighoffer, Andrei Alexandrescu

License

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at ).

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