feat: Day 2: Inventory Management System (part 2)

Author: mariotacke

day-02-inventory-management-system/README.md

@@ -24,5 +24,25 @@ Of these box IDs, four of them contain a letter which appears exactly twice, and
 
 **What is the checksum** for your list of box IDs?
 
+## Part Two
+
+Confident that your list of box IDs is complete, you're ready to find the boxes full of prototype fabric.
+
+The boxes will have IDs which differ by exactly one character at the same position in both strings. For example, given the following box IDs:
+
+```
+abcde
+fghij
+klmno
+pqrst
+fguij
+axcye
+wvxyz
+```
+
+The IDs `abcde` and `axcye` are close, but they differ by two characters (the second and fourth). However, the IDs `fghij` and `fguij` differ by exactly one character, the third (`h` and `u`). Those must be the correct boxes.
+
+**What letters are common between the two correct box IDs?** (In the example above, this is found by removing the differing character from either ID, producing `fgij`.)
+
 ## References
 - https://adventofcode.com/2018/day/2

day-02-inventory-management-system/common.js

@@ -0,0 +1,28 @@
+// get array without element at index i
+const without = (array, i) => [
+  ...array.slice(0, i),
+  ...array.slice(i + 1, array.length),
+];
+
+const common = (input) => {
+  const boxIds = input
+    .split('\n')
+    .map((x) => x.trim().split(''));
+
+  for (let i = 0; i < boxIds.length; i++) {
+    const boxId = boxIds[i];
+
+    for (let n = 0; n < boxId.length; n++) {
+      const boxForComparison = without(boxId, n).join('');
+
+      const ids = without(boxIds, i)
+        .map((id) => without(id, n).join(''));
+
+      if (ids.some((id) => id === boxForComparison)) {
+        return boxForComparison;
+      }
+    }
+  }
+};
+
+module.exports = common;

day-02-inventory-management-system/test.js

@@ -1,6 +1,7 @@
 const assert = require('assert');
 
 const checksum = require('./checksum');
+const common = require('./common');
 
 describe('Day 2: Inventory Management System', () => {
   it('should calculate checksum from box ids', () => {
@@ -15,4 +16,19 @@ describe('Day 2: Inventory Management System', () => {
 
     assert.strictEqual(checksum(boxIds), 12);
   });
+
+  describe('Part Two', () => {
+    it('should find common characters', () => {
+      const boxIds =
+        `abcde
+         fghij
+         klmno
+         pqrst
+         fguij
+         axcye
+         wvxyz`;
+
+      assert.strictEqual(common(boxIds), 'fgij');
+    });
+  });
 });