feat: 2016 Day 5

Add day 5 of 2016

Author: marcobiedermann

2016/day/3/index.test.ts

@@ -1,4 +1,4 @@
-import { readFileSync } from 'fs';
+import { readFileSync } from 'node:fs';
 import { part1, part2 } from '.';
 
 const input = readFileSync(`${__dirname}/input`, 'utf-8').split('\n');

2016/day/4/index.test.ts

@@ -1,9 +1,9 @@
-import { readFileSync } from 'fs';
+import { readFileSync } from 'node:fs';
 import { part1, part2 } from '.';
 
 const input = readFileSync(`${__dirname}/input`, 'utf-8').split('\n');
 
-describe('2016 Day 3', () => {
+describe('2016 Day 4', () => {
   describe('Part 1', () => {
     it('should sum the sector IDs of real rooms', () => {
       expect.assertions(2);

2016/day/5/README.md

@@ -0,0 +1,47 @@
+## --- Day 5: How About a Nice Game of Chess? ---
+
+You are faced with a security door designed by Easter Bunny engineers that seem to have acquired most of their security knowledge by watching [hacking](<https://en.wikipedia.org/wiki/Hackers_(film)>) [movies](https://en.wikipedia.org/wiki/WarGames).
+
+The _eight-character password_ for the door is generated one character at a time by finding the [MD5](https://en.wikipedia.org/wiki/MD5) hash of some Door ID (your puzzle input) and an increasing integer index (starting with `0`).
+
+A hash indicates the _next character_ in the password if its [hexadecimal](https://en.wikipedia.org/wiki/Hexadecimal) representation starts with _five zeroes_. If it does, the sixth character in the hash is the next character of the password.
+
+For example, if the Door ID is `abc`:
+
+- The first index which produces a hash that starts with five zeroes is `3231929`, which we find by hashing `abc3231929`; the sixth character of the hash, and thus the first character of the password, is `1`.
+- `5017308` produces the next interesting hash, which starts with `000008f82...`, so the second character of the password is `8`.
+- The third time a hash starts with five zeroes is for `abc5278568`, discovering the character `f`.
+
+In this example, after continuing this search a total of eight times, the password is `18f47a30`.
+
+Given the actual Door ID, _what is the password_?
+
+Your puzzle answer was `1a3099aa`.
+
+## --- Part Two ---
+
+As the door slides open, you are presented with a second door that uses a slightly more <span title="This one says 'WOPR' in block letters.">inspired</span> security mechanism. Clearly unimpressed by the last version (in what movie is the password decrypted _in order_?!), the Easter Bunny engineers have worked out [a better solution](https://www.youtube.com/watch?v=NHWjlCaIrQo&t=25).
+
+Instead of simply filling in the password from left to right, the hash now also indicates the _position_ within the password to fill. You still look for hashes that begin with five zeroes; however, now, the _sixth_ character represents the _position_ (`0`-`7`), and the _seventh_ character is the character to put in that position.
+
+A hash result of `000001f` means that `f` is the _second_ character in the password. Use only the _first result_ for each position, and ignore invalid positions.
+
+For example, if the Door ID is `abc`:
+
+- The first interesting hash is from `abc3231929`, which produces `0000015...`; so, `5` goes in position `1`: `_5______`.
+- In the previous method, `5017308` produced an interesting hash; however, it is ignored, because it specifies an invalid position (`8`).
+- The second interesting hash is at index `5357525`, which produces `000004e...`; so, `e` goes in position `4`: `_5__e___`.
+
+You almost choke on your popcorn as the final character falls into place, producing the password `05ace8e3`.
+
+Given the actual Door ID and this new method, _what is the password_? Be extra proud of your solution if it uses a cinematic "decrypting" animation.
+
+Your puzzle answer was `694190cd`.
+
+Both parts of this puzzle are complete! They provide two gold stars: \*\*
+
+At this point, you should [return to your Advent calendar](/2016) and try another puzzle.
+
+Your puzzle input was `uqwqemis`.
+
+You can also <span class="share">[Share<span class="share-content">on [Twitter](https://twitter.com/intent/tweet?text=I%27ve+completed+%22How+About+a+Nice+Game+of+Chess%3F%22+%2D+Day+5+%2D+Advent+of+Code+2016&url=https%3A%2F%2Fadventofcode%2Ecom%2F2016%2Fday%2F5&related=ericwastl&hashtags=AdventOfCode) [Mastodon](<javascript:void(0);>)</span>]</span> this puzzle.

2016/day/5/index.test.ts

@@ -0,0 +1,31 @@
+import { part1, part2 } from '.';
+
+const ONE_MINUTE_IN_MS = 1000 * 60;
+
+describe('2016 Day 5', () => {
+  describe('Part 1', () => {
+    it(
+      'should sum the sector IDs of real rooms',
+      () => {
+        expect.assertions(2);
+
+        expect(part1('abc')).toStrictEqual('18f47a30');
+        expect(part1('uqwqemis')).toStrictEqual('1a3099aa');
+      },
+      ONE_MINUTE_IN_MS,
+    );
+  });
+
+  describe('Part 2', () => {
+    it(
+      'should find the sector ID of the room where the northpole objects are being stored',
+      () => {
+        expect.assertions(2);
+
+        expect(part2('abc')).toStrictEqual('05ace8e3');
+        expect(part2('uqwqemis')).toStrictEqual('694190cd');
+      },
+      ONE_MINUTE_IN_MS,
+    );
+  });
+});

2016/day/5/index.ts

@@ -0,0 +1,46 @@
+import { createHash } from 'node:crypto';
+
+function part1(doorId: string): string {
+  const password: string[] = [];
+  let index = 0;
+
+  while (password.length < 8) {
+    const hash = createHash('md5')
+      .update(doorId + index)
+      .digest('hex');
+
+    if (hash.startsWith('00000')) {
+      password.push(hash[5]);
+    }
+
+    index += 1;
+  }
+
+  return password.join('');
+}
+
+function part2(doorId: string): string {
+  const password: string[] = [];
+  let index = 0;
+
+  while (password.length < 8) {
+    const hash = createHash('md5')
+      .update(doorId + index)
+      .digest('hex');
+
+    if (hash.startsWith('00000')) {
+      const position = parseInt(hash[5], 10);
+
+      if (position < 8 && !password[position]) {
+        // eslint-disable-next-line prefer-destructuring
+        password[position] = hash[6];
+      }
+    }
+
+    index += 1;
+  }
+
+  return password.join('');
+}
+
+export { part1, part2 };

README.md

@@ -176,7 +176,7 @@ My attempt of solving [Advent of Code](https://adventofcode.com/) puzzles in Jav
 | [Day 8](2016/day/8)   |       |
 | [Day 7](2016/day/7)   |       |
 | [Day 6](2016/day/6)   |       |
-| [Day 5](2016/day/5)   |       |
+| [Day 5](2016/day/5)   | ⭐⭐  |
 | [Day 4](2016/day/4)   | ⭐⭐  |
 | [Day 3](2016/day/3)   | ⭐    |
 | [Day 2](2016/day/2)   | ⭐⭐  |