Table of Contents
This was a fairly easy problem to solve compared to the previous one – bracket push, which took me 2 hours to solve after going down the wrong path and not realizing the correct approach.
Live solution video
This is my daily live stream video solution to this problem.
- Video available here: https://youtu.be/kvUtVYnraPk
- Also streaming on Twitch: https://www.twitch.tv/percygrunwald
Explanation of the solution
Map of DNA nucleotide charcodes to RNA nucleotide charcodes
The bulk of the heavy lifting in this solution comes from the map of DNA nucleotide charcodes to RNA nucleotide charcodes:
@dna_nucleotide_to_rna_nucleotide_map %{
# `G` -> `C`
71 => 67,
# `C` -> `G`
67 => 71,
# `T` -> `A`
84 => 65,
# `A` -> `U`
65 => 85
}
These mappings came directly from the README:
Given a DNA strand, its transcribed RNA strand is formed by replacing
each nucleotide with its complement:
* `G` -> `C`
* `C` -> `G`
* `T` -> `A`
* `A` -> `U`
If you’re curious how to get the charcodes, you can use IO.inspect/2 with the charlists: false option:
iex> IO.inspect('GCTAU', charlists: false)
[71, 67, 84, 65, 85]
'GCTAU'
Function to map a DNA nucleotide charlist to RNA nucleotide charlist
The function to map the charlist of DNA nucleotides to RNA nucleotides is really simple, it’s just an Enum.map/2 over the charcodes in the DNA nucleotide charlist:
@spec to_rna([char]) :: [char]
def to_rna(dna) do
dna
|> Enum.map(&get_rna_for_dna/1)
end
defp get_rna_for_dna(dna_nucleotide) do
@dna_nucleotide_to_rna_nucleotide_map[dna_nucleotide]
end
Enum.map/2 calls the get_rna_for_dna/1 function for each charcode. get_rna_for_dna/1 simply does a lookup in @dna_nucleotide_to_rna_nucleotide_map, which we defined earlier.
For example, if we call get_rna_for_dna(71) it will return 67 (71 being the charcode for G and 67 being the charcode forC`).
Full solution in text form
Here’s the full solution in text form, in case you want to look over the final product:
defmodule RNATranscription do
@dna_nucleotide_to_rna_nucleotide_map %{
# `G` -> `C`
71 => 67,
# `C` -> `G`
67 => 71,
# `T` -> `A`
84 => 65,
# `A` -> `U`
65 => 85
}
@doc """
Transcribes a character list representing DNA nucleotides to RNA
## Examples
iex> RNATranscription.to_rna('ACTG')
'UGAC'
"""
@spec to_rna([char]) :: [char]
def to_rna(dna) do
dna
|> Enum.map(&get_rna_for_dna/1)
end
defp get_rna_for_dna(dna_nucleotide) do
@dna_nucleotide_to_rna_nucleotide_map[dna_nucleotide]
end
end