feat(2020-day-05): calculate seat details from seat code

seat code is basically a bitmap. converting to binary and casting
to integers makes it a lot simpler to figure out the details without
having to think about it

Author: developher-net

2020/day-05/seats.js

@@ -0,0 +1,30 @@
+// Seat codes are basically bitmaps, so convert them
+const seatCodeToBitmap = (seatCode) => {
+  return seatCode
+    .replace(/F/g, 0)
+    .replace(/B/g, 1)
+    .replace(/L/g, 0)
+    .replace(/R/g, 1)
+}
+
+const calcSeatId = ({ row, column }) => row * 8 + column
+
+const getSeat = (seatCode) => {
+  // Seat codes are basically bitmaps, so convert them
+  const seatBitMap = seatCodeToBitmap(seatCode)
+
+  // First octect is row
+  const row = parseInt(seatBitMap.slice(0, 7), 2)
+  // Last triplet is column
+  const column = parseInt(seatBitMap.slice(7), 2)
+
+  return {
+    row,
+    column,
+    id: calcSeatId({ row, column })
+  }
+}
+
+module.exports = {
+  getSeat
+}

2020/day-05/seats.test.js

@@ -0,0 +1,27 @@
+/* eslint-env mocha */
+const { expect } = require('chai')
+const { getSeat } = require('./seats')
+
+describe('--- Day 5: Binary Boarding ---', () => {
+  describe('Part 1', () => {
+    describe('getSeat()', () => {
+      it('returns the seat details for a given seat code', () => {
+        expect(getSeat('BFFFBBFRRR')).to.deep.equal({
+          row: 70,
+          column: 7,
+          id: 567
+        })
+        expect(getSeat('FFFBBBFRRR')).to.deep.equal({
+          row: 14,
+          column: 7,
+          id: 119
+        })
+        expect(getSeat('BBFFBBFRLL')).to.deep.equal({
+          row: 102,
+          column: 4,
+          id: 820
+        })
+      })
+    })
+  })
+})