Nucleotide Count

typescript/nucleotide-count/nucleotide-count.test.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect, xit } from '@jest/globals'
+import { describe, expect, it } from '@jest/globals'
 import { nucleotideCounts } from './nucleotide-count.ts'
 
 describe('count all nucleotides in a strand', () => {
@@ -12,7 +12,7 @@ describe('count all nucleotides in a strand', () => {
     expect(nucleotideCounts('')).toEqual(expected)
   })
 
-  xit('can count one nucleotide in single-character input', () => {
+  it('can count one nucleotide in single-character input', () => {
     const expected = {
       A: 0,
       C: 0,
@@ -22,7 +22,7 @@ describe('count all nucleotides in a strand', () => {
     expect(nucleotideCounts('G')).toEqual(expected)
   })
 
-  xit('strand with repeated nucleotide', () => {
+  it('strand with repeated nucleotide', () => {
     const expected = {
       A: 0,
       C: 0,
@@ -32,7 +32,7 @@ describe('count all nucleotides in a strand', () => {
     expect(nucleotideCounts('GGGGGGG')).toEqual(expected)
   })
 
-  xit('strand with multiple nucleotides', () => {
+  it('strand with multiple nucleotides', () => {
     const expected = {
       A: 20,
       C: 12,
@@ -46,7 +46,7 @@ describe('count all nucleotides in a strand', () => {
     ).toEqual(expected)
   })
 
-  xit('strand with invalid nucleotides', () => {
+  it('strand with invalid nucleotides', () => {
     const expected = 'Invalid nucleotide in strand'
     expect(() => {
       nucleotideCounts('AGXXACT')

typescript/nucleotide-count/nucleotide-count.ts

@@ -1,3 +1,21 @@
-export function nucleotideCounts(/* Parameters go here */) {
-  throw new Error('Remove this statement and implement this function')
+const nucleotides = ['A', 'C', 'G', 'T'] as const
+type Nucleotide = typeof nucleotides[number]
+type NucleotideCounts = Record<Nucleotide, number>
+
+function isNucleotide(char: string): char is Nucleotide {
+  return (nucleotides as readonly string[]).includes(char)
 }
+
+export const nucleotideCounts = (nucleotide: string): NucleotideCounts =>
+  nucleotide.split("").map(char => 
+     (!isNucleotide(char))
+      ? (() => { throw new Error('Invalid nucleotide in strand')})()
+      : char
+  ).reduce((result, char) => ({
+    ...result, [char]: result[char] + 1
+  }), {
+      A: 0,
+      C: 0,
+      G: 0,
+      T: 0,
+    })