Menengah Exercism • kotlin

Nucleotide Count

Ringkasan Tantangan

Given a DNA string, compute how many times each nucleotide occurs in the string.

Instructions

Each of us inherits from our biological parents a set of chemical instructions known as DNA that influence how our bodies are constructed. All known life depends on DNA!

Note: You do not need to understand anything about nucleotides or DNA to complete this exercise.

DNA is a long chain of other chemicals and the most important are the four nucleotides, adenine, cytosine, guanine and thymine. A single DNA chain can contain billions of these four nucleotides and the order in which they occur is important! We call the order of these nucleotides in a bit of DNA a “DNA sequence”.

We represent a DNA sequence as an ordered collection of these four nucleotides and a common way to do that is with a string of characters such as “ATTACG” for a DNA sequence of 6 nucleotides. ‘A’ for adenine, ‘C’ for cytosine, ‘G’ for guanine, and ‘T’ for thymine.

Given a string representing a DNA sequence, count how many of each nucleotide is present. If the string contains characters that aren’t A, C, G, or T then it is invalid and you should signal an error.

For example:

"GATTACA" -> 'A': 3, 'C': 1, 'G': 1, 'T': 2
"INVALID" -> error

Dig Deeper

groupBy with +

`groupBy` with `+`

class Dna(val sequence: String) {
    init {
        require(sequence.all { it in "ACGT" })
    }
    val nucleotideCounts
        get() = mapOf('A' to 0, 'C' to 0, 'G' to 0, 'T' to 0) + sequence.groupingBy { it }.eachCount()
}

Verification

We receive a sequence as input, which we have to verify. Because the sequence is part of the primary constructor, which can’t contain runnable code, we have to place the check in an initializer block. In Kotlin it’s idiomatic to use the require keyword for verification. require will throw an IllegalArgumentException if the given value is false.

init {
    require(sequence.all { it in "ACGT" })
}

Base Map

We define a base map with a zero value for every nucleotide. We do this to ensure that every nucleotide will be present in the output, even if there is no count. Afterward we can overwrite some of the values by using the + operator. Note that the + operator on maps does not add the values but overwrites them.

val nucleotideCounts
    get() = mapOf('A' to 0, 'C' to 0, 'G' to 0, 'T' to 0)

Counting Nucleotides

We use the .groupingBy function to create a Grouping of the nucleotides. By using the .eachCount() function we turn the Grouping in a Map. For example: "ACA".groupingBy { it }.eachCount() results in {A=2, C=1}. After adding the maps together we receive our final answer.

val nucleotideCounts
    get() = mapOf('A' to 0, 'C' to 0, 'G' to 0, 'T' to 0) + sequence.groupingBy { it }.eachCount()

Source: Exercism kotlin/nucleotide-count

💡 Lihat Solusi

class Dna (sequence: String) {
    init {
        require(sequence.all { c -> c in "ACGT" })
    }

    val nucleotideCounts: Map<Char, Int> = sequence.groupBy { it }
            .mapValuesTo(mutableMapOf('A' to 0,'C' to 0, 'G' to 0, 'T' to 0)) { it.value.size }
}