exercism/elixir/paint-by-number/HINTS.md

Hints

General

• Read about bitstrings in the Getting Started guide.
• Review the documentation for the bitstring special form.
• Review how to convert decimal numbers to binary numbers.
• Elixir supports different ways of writing integers, including binary notation.

1. Calculate palette bit size

• This task doesn't use the bitstring data type.
• 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.
• Create a recursive function for this.
• 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).
• Use Integer.pow/2 to raise 2 to a given power.

2. Create an empty picture

• Use the bitstring special form to create a new bitstring.

3. Create a test picture

• Use the bitstring special form to create a new bitstring.
• Use the type operator to specify the bit size of each fragment.

4. Prepend a pixel to a picture

• The bitstring special form can be used to append a new fragment to an existing bitstring.
• Use the type operator to specify the bit size of the new fragment as well as the existing bitstring.
• Use the previously implemented PaintByNumber.palette_bit_size/1 function to get the bit size of the new fragment.
• Use the special ::bitstring type to specify that the old fragment is of unknown size.

5. Get the first pixel from a picture

• The bitstring special form can be used to pattern match bitstrings.
• Use the previously implemented PaintByNumber.palette_bit_size/1 function to get the bit size of one pixel.
• Use the special ::bitstring type to specify that the rest of the bitstring is of unknown size.

6. Drop the first pixel from a picture

• The bitstring special form can be used to pattern match bitstrings.
• Use the previously implemented PaintByNumber.palette_bit_size/1 function to get the bit size of one pixel.
• Use the special ::bitstring type to specify that the rest of the bitstring is of unknown size.

7. Concatenate two pictures

• The bitstring special form can be used to concatenate two bitstrings.
• Use the special ::bitstring type to specify that each of the bitstring fragments is of unknown size.