## to Nucleotide Count in the TypeScript Track

Published at Jun 28 2019 · 0 comments
Instructions
Test suite
Solution

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

The genetic language of every living thing on the planet is DNA. DNA is a large molecule that is built from an extremely long sequence of individual elements called nucleotides. 4 types exist in DNA and these differ only slightly and can be represented as the following symbols: 'A' for adenine, 'C' for cytosine, 'G' for guanine, and 'T' thymine.

Here is an analogy:

• twigs are to birds nests as
• nucleotides are to DNA as
• legos are to lego houses as
• words are to sentences as...

## Setup

Go through the setup instructions for TypeScript to install the necessary dependencies:

https://exercism.io/tracks/typescript/installation

## Requirements

Install assignment dependencies:

``````\$ yarn install
``````

## Making the test suite pass

Execute the tests with:

``````\$ yarn test
``````

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by changing `xit` to `it`.

## Source

The Calculating DNA Nucleotides_problem at Rosalind http://rosalind.info/problems/dna/

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### nucleotide-count.test.ts

``````import NucleotideCount from './nucleotide-count'

describe('count all nucleotides in a strand', () => {
it('empty strand', () => {
const expected = {
A: 0,
C: 0,
G: 0,
T: 0
}
expect(NucleotideCount.nucleotideCounts('')).toEqual(expected)
})

xit('can count one nucleotide in single-character input', () => {
const expected = {
A: 0,
C: 0,
G: 1,
T: 0
}
expect(NucleotideCount.nucleotideCounts('G')).toEqual(expected)
})

xit('strand with repeated nucleotide', () => {
const expected = {
A: 0,
C: 0,
G: 7,
T: 0
}
expect(NucleotideCount.nucleotideCounts('GGGGGGG')).toEqual(expected)
})

xit('strand with multiple nucleotides', () => {
const expected = {
A: 20,
C: 12,
G: 17,
T: 21
}
expect(NucleotideCount.nucleotideCounts('AGCTTTTCATTCTGACTGCAACGGGCAATATGTCTCTGTGTGGATTAAAAAAAGAGTGTCTGATAGCAGC')).toEqual(expected)
})

xit('strand with invalid nucleotides', () => {
const expected = 'Invalid nucleotide in strand'
expect(() => {NucleotideCount.nucleotideCounts('AGXXACT')}).toThrowError(expected)
})
})``````
``````const DefaultNucleotideCount = { A: 0, C: 0, G: 0, T: 0 }
type NucleotideCountResult = { [key in keyof typeof DefaultNucleotideCount]: number }

class NucleotideCount {
static nucleotideCounts(dna: string): NucleotideCountResult {
let result = Object.assign({}, DefaultNucleotideCount)
for (const nucleotide of dna) {
switch (nucleotide) {
case 'A': result.A += 1; break;
case 'C': result.C += 1; break;
case 'G': result.G += 1; break;
case 'T': result.T += 1; break;
default: throw new Error('Invalid nucleotide in strand')
}
}
return result
}
}

export default NucleotideCount``````