feat(2021-day-08): count occurrences of numbers 1,4,7,8 in scrambled …

…signals

solves part 1

2021/day-08/display.js

@@ -28,6 +28,36 @@
 //   })
 //   }
 
+/**
+ * Using a map of character codes, decode a signal
+ * @param {array} charCodes
+ * @param {string} signal
+ */
+const decodeSignal = (charCodes, signal) => {
+  console.debug('2021-day-08 decodeSignal()')
+
+  const digits = signal.split(' ')
+    .map(
+      (code) => {
+        const clean = code.split('').sort() // cleanup format to match expected map of codes
+        const matches = charCodes.filter((c) => {
+          // sort here on the charCode is just in case non-alphabatized data is provided
+          return (JSON.stringify(c.sort()) === JSON.stringify(clean))
+        })
+        if (matches.length < 1) {
+          throw new Error(`No match found for ${code} when cleaned up to ${clean}`)
+        }
+        if (matches.length > 1) {
+          throw new Error(`Too many matches for ${code} when cleaned up to ${clean}. This most likely indicates a bad list of character codes.`)
+        }
+
+        // The key in charCodes for the match is the decoded number we want
+        return charCodes.indexOf(matches[0])
+      }
+    )
+
+  return digits
+}
 
 /**
  * Takes a string of scrambled codes and deduces which codes correspond
@@ -454,5 +484,6 @@ const descrambleSignal = (data) => {
 }
 
 module.exports = {
+  decodeSignal,
   descrambleSignal
 }

2021/day-08/display.test.js

@@ -1,9 +1,20 @@
 /* eslint-env mocha */
 const { expect } = require('chai')
-const { descrambleSignal } = require('./display')
+const { descrambleSignal, decodeSignal } = require('./display')
 
 const testSingle = 'acedgfb cdfbe gcdfa fbcad dab cefabd cdfgeb eafb cagedb ab | cdfeb fcadb cdfeb cdbaf'
 
+const testMultiple = `be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb | fdgacbe cefdb cefbgd gcbe
+edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec | fcgedb cgb dgebacf gc
+fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg
+fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega | efabcd cedba gadfec cb
+aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga | gecf egdcabf bgf bfgea
+fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf | gebdcfa ecba ca fadegcb
+dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf | cefg dcbef fcge gbcadfe
+bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbgef
+egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb
+gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce`.split('\n')
+
 console.debug(
   testSingle.split('|')[0].trim()
     .split(' ').map(
@@ -31,5 +42,35 @@ describe('--- Day 8: Seven Segment Search ---', () => {
         expect(charCodes.map(code => code.length)).to.deep.equal(expectedLengths)
       })
     })
+    describe('decodeSignal()', () => {
+      const testData = testMultiple[0].split('|').map((a) => a.trim())
+      const { charCodes } = descrambleSignal(testData[0])
+
+      it('decodes a display pattern using the provided map of display codes', () => {
+        const result = decodeSignal(charCodes, testData[1])
+        expect(result[0]).to.equal(8)
+        expect(result[3]).to.equal(4)
+      })
+      it('throws an error if a digit doesn`t have a matching code', () => {
+        expect(
+          () => decodeSignal(
+            [['a']],
+            'dcb'
+          )
+        ).to.throw(
+          'No match found for dcb when cleaned up to b,c,d'
+        )
+      })
+      it('throws an error if a digit has multiple matches (meaning a bad codes map)', () => {
+        expect(
+          () => decodeSignal(
+            [['a'], ['d', 'c', 'b'], ['b', 'c', 'd']],
+            'dcb'
+          )
+        ).to.throw(
+          'Too many matches for dcb when cleaned up to b,c,d. This most likely indicates a bad list of character codes.'
+        )
+      })
+    })
   })
 })

2021/day-08/solution.js

@@ -1,22 +1,38 @@
 const fs = require('fs')
 const path = require('path')
 const filePath = path.join(__dirname, 'input.txt')
-const { inputToArray } = require('../../2018/inputParser')
+const { linesToArray } = require('../../2018/inputParser')
+const { descrambleSignal, decodeSignal } = require('./display')
 
 fs.readFile(filePath, { encoding: 'utf8' }, (err, initData) => {
   if (err) throw err
 
-  initData = inputToArray(initData.trim())
+  initData = linesToArray(initData.trim())
 
   const resetInput = () => {
     // Deep copy to ensure we aren't mutating the original data
-    return JSON.parse(JSON.stringify(initData))
+    return JSON.parse(JSON.stringify(
+      initData.map(
+        (line) => line.split('|')
+          .map((e) => e.trim())
+      )
+    ))
   }
 
   const part1 = () => {
     const data = resetInput()
-    console.debug(data)
-    return 'No answer yet'
+
+    return data.map((entry) => {
+      const { charCodes } = descrambleSignal(entry[0])
+      return decodeSignal(charCodes, entry[1])
+    }).reduce((total, signal) => {
+      const search = [1, 4, 7, 8]
+
+      // Find how many of our desired numbers are in the signal
+      total += signal.filter((digit) => search.includes(digit)).length
+
+      return total
+    }, 0)
   }
 
   const part2 = () => {

index.js

@@ -1 +1 @@
-require('./2021/day-07/solution')
+require('./2021/day-08/solution')