Nucleotide Count

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,
+    })