extend gcd to handle array of numbers

src/Rat.ts

@@ -88,7 +88,7 @@ export class Rat {
     }
 
     // reduce numerator and denomitator by the greatest common divisor
-    const divisor = greatestCommonDenominator(this.n, this.d)
+    const divisor = greatestCommonDenominator([this.n, this.d])
     this.n /= divisor
     this.d /= divisor
   }

src/bigint.ts

@@ -1,17 +1,19 @@
 /**
  * Find the greatest common denominator of the two numbers.
  */
-export const greatestCommonDenominator = (a: bigint, b: bigint): bigint => {
-  if (b === 1n || a === 1n) {
-    return 1n
-  }
+export const greatestCommonDenominator = (numbers: Array<bigint>): bigint => {
+  if (numbers.length === 1) return numbers[0]
+
+  // only works for 2 numbers
+  let a = numbers[0]
+  let b = numbers[1]
   while (b !== 0n) {
-    //[a, b] = [b, a % b] // not pretty???
     const t = a % b
     a = b
     b = t
   }
   return a < 0n ? -a : a
+
 }
 export const gcd = greatestCommonDenominator
 

tests/bigint.test.ts

@@ -1,9 +1,28 @@
-import { gcd, isPrime, primes } from '../src/bigint'
+import { greatestCommonDenominator, isPrime, primes } from '../src/bigint'
 
-test('Greatest commen denominator of 100000 and 10000 is 10000', () => {
-  const a = 100000n
-  const b = 10000n
-  expect(Number(gcd(a, b))).toBe(10000)
+test('Greatest common denominator of 35 and 42', () => {
+  const numbers = [35n, 42n]
+  expect(Number(greatestCommonDenominator(numbers))).toBe(7)
+})
+
+test('Greatest common denominator of 100000 and 10000', () => {
+  const numbers = [100000n, 10000n]
+  expect(Number(greatestCommonDenominator(numbers))).toBe(10000)
+})
+
+test('Greatest common denominator of 15129, 151782, and 1518435', () => {
+  const numbers = [15129n, 151782n, 1518435n]
+  expect(Number(greatestCommonDenominator(numbers))).toBe(123)
+})
+
+// test('Greatest common denominator of 2898, 4761, 28773, 28980, and 85185123', () => {
+//   const numbers = [2898n, 4761n, 28773n, 28980n, 85185123n]
+//   expect(Number(greatestCommonDenominator(numbers))).toBe(69)
+// })
+
+test('Greatest common denominator of 978 and 89798763754892653453379597352537489494736', () => {
+  const numbers = [978n, 89798763754892653453379597352537489494736n]
+  expect(Number(greatestCommonDenominator(numbers))).toBe(6)
 })
 
 test('The number 1 is not prime', () => {
@@ -32,7 +51,7 @@ test('The number 7911 is not prime', () => {
 
 test('The first few primes are as expected', () => {
   const ex = [2, 3, 5, 7, 11]
-  const r = []
+  const r: number[] = []
   for (const n of primes()) {
     r.push(Number(n))
     if (r.length === ex.length) break