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to Nucleotide Count in the TypeScript Track

Published at Jul 09 2019 · 0 comments
Test suite

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...


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



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.


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.


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

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

  xit('strand with repeated nucleotide', () => {
    const expected = {
      A: 0,
      C: 0,
      G: 7,
      T: 0

  xit('strand with multiple nucleotides', () => {
    const expected = {
      A: 20,
      C: 12,
      G: 17,
      T: 21

  xit('strand with invalid nucleotides', () => {
    const expected = 'Invalid nucleotide in strand'
    expect(() => {NucleotideCount.nucleotideCounts('AGXXACT')}).toThrowError(expected)
class NucleotideCount {
  static nucleotideCounts(input:string) {
    // Your code here
    let result: {[key: string]: number} = {A:0, C:0, G:0, T:0};

    input.split("").forEach(function(element) {
      if (element in result){
        result[element] += 1;
      } else{
        throw new Error("Invalid nucleotide in strand");
    return result;

export default NucleotideCount

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