feat(2021-day-03): calculate oxygen/carbon dioxide values for life support

Solves part 2

Author: developher-net

2021/day-03/engineDiagnostics.js

@@ -7,8 +7,8 @@ const getMostCommon = (data, position) => {
   const offs = data.filter((reading) => {
     return reading[position] === '0'
   }).length
-  // there can only be 2 values, so easy to check which has more as being 50% or above
-  return (offs >= data.length / 2) ? '0' : '1'
+  // there can only be 2 values, so easy to check which has more as being above 50%
+  return (offs > data.length / 2) ? '0' : '1'
 }
 
 /**
@@ -40,6 +40,36 @@ const getEpsilon = (data) => {
   return epsilon
 }
 
+const getO2 = (data) => {
+  return getAir(data, getMostCommon)
+}
+
+const getCO2 = (data) => {
+  return getAir(data, getLeastCommon)
+}
+
+const getAir = (data, filterMethod) => {
+  let dataset = data
+  // Loop through each digit, find the most common bit for that digit, and filter
+  // out any readings that don't share that digit
+  //
+  // TODO: Probably faster with bitmap math, but .... ehh... runs fast enough
+  for (let x = 0; x < data[0].length; x++) {
+    if (dataset.length > 1) {
+      const bit = filterMethod(dataset, x)
+      dataset = dataset.filter((reading) => {
+        return reading[x] === bit
+      })
+    }
+  }
+
+  if (dataset.length > 1) {
+    throw new Error(`Found too many results ${dataset}`)
+  }
+
+  return dataset[0]
+}
+
 const calcPowerConsumption = (gamma, epsilon) => {
   return parseInt(gamma, 2) * parseInt(epsilon, 2)
 }
@@ -49,5 +79,8 @@ module.exports = {
   getEpsilon,
   getMostCommon,
   getLeastCommon,
-  calcPowerConsumption
+  getO2,
+  getCO2,
+  calcPowerConsumption,
+  calcLifeSupport: calcPowerConsumption
 }

2021/day-03/engineDiagnostics.test.js

@@ -1,6 +1,6 @@
 /* eslint-env mocha */
 const { expect } = require('chai')
-const { getMostCommon, getLeastCommon, getEpsilon, getGamma, calcPowerConsumption } = require('./engineDiagnostics')
+const { getMostCommon, getLeastCommon, getEpsilon, getGamma, getO2, getCO2, calcPowerConsumption, calcLifeSupport } = require('./engineDiagnostics')
 
 const testData = [
   '00100',
@@ -53,4 +53,21 @@ describe('--- Day 3: Binary Diagnostic ---', () => {
       })
     })
   })
+  describe('Part 2', () => {
+    describe('getO2()', () => {
+      it('calculates the oxygen generator rating from the provided data', () => {
+        expect(getO2(testData)).to.equal('10111')
+      })
+    })
+    describe('getCO2()', () => {
+      it('calculates the carbon dioxide scrubber rating from the provided data', () => {
+        expect(getCO2(testData)).to.equal('01010')
+      })
+    })
+    describe('calcLifeSupport', () => {
+      it('calculates the life support rating by multiplying the O2 and C02 rates rates as decimals', () => {
+        expect(calcLifeSupport('10110', '01001')).to.equal(198)
+      })
+    })
+  })
 })

2021/day-03/solution.js

@@ -2,7 +2,7 @@ const fs = require('fs')
 const path = require('path')
 const filePath = path.join(__dirname, 'input.txt')
 const { inputToArray } = require('../../2018/inputParser')
-const { getGamma, getEpsilon, calcPowerConsumption } = require('./engineDiagnostics')
+const { getGamma, getEpsilon, calcPowerConsumption, calcLifeSupport, getO2, getCO2 } = require('./engineDiagnostics')
 
 fs.readFile(filePath, { encoding: 'utf8' }, (err, initData) => {
   if (err) throw err
@@ -24,8 +24,10 @@ fs.readFile(filePath, { encoding: 'utf8' }, (err, initData) => {
 
   const part2 = () => {
     const data = resetInput()
-    console.debug(data)
-    return 'No answer yet'
+    return calcLifeSupport(
+      getO2(data),
+      getCO2(data)
+    )
   }
   const answers = []
   answers.push(part1())