refactor: 2015 Day 4

Refactor day 4 of 2015

2015/day/4/index.test.ts

@@ -3,20 +3,20 @@ import { part1, part2 } from '.';
 
 const input = 'ckczppom';
 
-describe('Day 4', () => {
-  describe('Part 1', () => {
-    it('should find a hash which starts with five zeros', () => {
-      expect.assertions(1);
-
-      expect(part1(input)).toStrictEqual(117946);
+describe('2015', () => {
+  describe('Day 4', () => {
+    describe('Part 1', () => {
+      it('should find a hash which starts with five zeros', () => {
+        expect(part1('abcdef')).toBe(609043);
+        expect(part1('pqrstuv')).toBe(1048970);
+        expect(part1(input)).toBe(117946);
+      });
     });
-  });
-
-  describe('Part 2', () => {
-    it('should find a hash which starts with six zeros', () => {
-      expect.assertions(1);
 
-      expect(part2(input)).toStrictEqual(3938038);
+    describe('Part 2', () => {
+      it('should find a hash which starts with six zeros', () => {
+        expect(part2(input)).toBe(3938038);
+      });
     });
   });
 });

2015/day/4/index.ts

@@ -1,13 +1,19 @@
-import crypto from 'crypto';
+import crypto from 'node:crypto';
+
+const ZERO = '0' as const;
+
+function getMd5Hash(input: string): string {
+  return crypto.createHash('md5').update(input).digest('hex');
+}
 
 function part1(key: string, digits = 5): number {
+  const str = ZERO.repeat(digits);
   let index = 1;
 
   while (true) {
-    const input = `${key}${index}`;
-    const hash = crypto.createHash('md5').update(input).digest('hex');
+    const hash = getMd5Hash(`${key}${index}`);
 
-    if (hash.slice(0, digits) === '0'.repeat(digits)) {
+    if (hash.startsWith(str)) {
       return index;
     }