57 lines
3.2 KiB
Markdown
57 lines
3.2 KiB
Markdown
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# Hints
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## General
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- Read about [bitstrings][bitstring] in the Getting Started guide.
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- Review the documentation for the [bitstring special form][bitstring-form].
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- Review [how to convert decimal numbers to binary numbers][decimal-to-binary-youtube].
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- Elixir supports [different ways of writing integers][integer-literal], including binary notation.
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## 1. Calculate palette bit size
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- This task doesn't use the bitstring data type.
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- Find the smallest positive number `n` such that 2 raised to the power of `n` is greater than or equal than the number of colors we need to represent.
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- Create a recursive function for this.
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- Choose a starting bit size of 1. If 2 raised to the power of the bit size is greater than or equal to the color count, we've found our bit size. If not, add 1 to the bit size and check again (recursion).
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- Use [`Integer.pow/2`][integer-pow] to raise 2 to a given power.
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## 2. Create an empty picture
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- Use the [bitstring special form][bitstring-form] to create a new bitstring.
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## 3. Create a test picture
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- Use the [bitstring special form][bitstring-form] to create a new bitstring.
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- Use the [type operator][type-operator] to specify the bit size of each fragment.
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## 4. Prepend a pixel to a picture
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- The [bitstring special form][bitstring-form] can be used to append a new fragment to an existing bitstring.
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- Use the [type operator][type-operator] to specify the bit size of the new fragment as well as the existing bitstring.
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- Use the previously implemented `PaintByNumber.palette_bit_size/1` function to get the bit size of the new fragment.
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- Use the special `::bitstring` type to specify that the old fragment is of unknown size.
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## 5. Get the first pixel from a picture
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- The [bitstring special form][bitstring-form] can be used to [pattern match bitstrings][bitstring-matching].
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- Use the previously implemented `PaintByNumber.palette_bit_size/1` function to get the bit size of one pixel.
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- Use the special `::bitstring` type to specify that the rest of the bitstring is of unknown size.
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## 6. Drop the first pixel from a picture
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- The [bitstring special form][bitstring-form] can be used to [pattern match bitstrings][bitstring-matching].
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- Use the previously implemented `PaintByNumber.palette_bit_size/1` function to get the bit size of one pixel.
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- Use the special `::bitstring` type to specify that the rest of the bitstring is of unknown size.
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## 7. Concatenate two pictures
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- The [bitstring special form][bitstring-form] can be used to concatenate two bitstrings.
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- Use the special `::bitstring` type to specify that each of the bitstring fragments is of unknown size.
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[decimal-to-binary-youtube]: https://www.youtube.com/watch?v=gGiEu7QTi68
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[integer-literal]: https://hexdocs.pm/elixir/syntax-reference.html#integers-in-other-bases-and-unicode-code-points
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[bitstring]: https://elixir-lang.org/getting-started/binaries-strings-and-char-lists.html#bitstrings
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[bitstring-form]: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#%3C%3C%3E%3E/1
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[bitstring-matching]: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#%3C%3C%3E%3E/1-binary-bitstring-matching
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[type-operator]: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#::/2
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[integer-pow]: https://hexdocs.pm/elixir/Integer.html#pow/2
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