James Harton
2f8eaa0f61
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102 lines
3 KiB
Markdown
102 lines
3 KiB
Markdown
# Heap
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[](https://drone.harton.dev/james/heap)
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[](https://hex.pm/packages/heap)
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[](https://firstdonoharm.dev/version/3/0/full.html)
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A Heap is a very useful data structure, because it sorts, quickly, at insert time.
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See also: https://en.wikipedia.org/wiki/Heap_(data_structure)
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You can use it for things like:
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- Help with scientific computing
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- Quickly sorting
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- Priority queues
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## Installation
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Heap is [available in Hex](https://hex.pm/packages/heap), the package can be
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installed by adding `heap` to your list of dependencies in `mix.exs`:
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```elixir
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def deps do
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[
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{:heap, "~> 3.0.0"}
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]
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end
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```
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Documentation for the latest release can be found on
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[HexDocs](https://hexdocs.pm/heap) and for the `main` branch on
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[docs.harton.nz](https://docs.harton.nz/james/heap).
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## Deprecation warning
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If you're upgrading from `heap` < 2.0 be aware that the direction of the `:<`
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and `:>` atoms passed into `Heap.new/1` has changed to make more sense.
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## Examples
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Create a min heap and use it to find the smallest element in a collection:
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```elixir
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1..500 |> Enum.shuffle |> Enum.into(Heap.min) |> Heap.root
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# => 1
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```
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Likewise, for max heaps:
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```elixir
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1..500 |> Enum.shuffle |> Enum.into(Heap.max) |> Heap.root
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# => 500
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```
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A priority queue:
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Tuples are compared by their elements in order, so you can push tuples
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of `{priority, term}` into a Heap for sorting by priority:
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```elixir
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Heap.new
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|> Heap.push({4, :jam})
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|> Heap.push({1, :milk})
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|> Heap.push({2, :eggs})
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|> Heap.push({1, :bread})
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|> Heap.push({3, :butter})
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|> Heap.push({2, :coffee})
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|> Enum.map(fn {_, what} -> what end)
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# => [:bread, :milk, :coffee, :eggs, :butter, :jam]
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```
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The heap can also be constructed with a custom comparator:
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```elixir
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Heap.new(&(Date.compare(elem(&1, 0), elem(&2, 0)) == :gt))
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|> Heap.push({~D[2017-11-20], :jam})
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|> Heap.push({~D[2017-11-21], :milk})
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|> Heap.push({~D[2017-10-21], :bread})
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|> Heap.push({~D[2017-10-20], :eggs})
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|> Enum.map(fn {_, what} -> what end)
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# => [:milk, :jam, :bread, :eggs]
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```
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To access the root and the rest of the heap in one line use `Heap.split/1`:
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```elixir
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{root, rest} = Heap.split(heap)
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{root, rest} == {Heap.root(heap), Heap.pop(heap)}
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# => true
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```
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## License
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This software is licensed under the terms of the
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[HL3-FULL](https://firstdonoharm.dev), see the `LICENSE.md` file included with
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this package for the terms.
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This license actively proscribes this software being used by and for some
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industries, countries and activities. If your usage of this software doesn't
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comply with the terms of this license, then [contact me](mailto:james@harton.nz)
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with the details of your use-case to organise the purchase of a license - the
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cost of which may include a donation to a suitable charity or NGO.
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