feat(2019-day-02): solution for part 2

Brute force the combination of acceptable program inputs until the desired
program output is reached

Author: developher-net

2019/day-02/solution.js

@@ -4,17 +4,66 @@ const filePath = path.join(__dirname, 'input.txt')
 const { runProgram } = require('./intcodeParser')
 const { inputToArray } = require('../../2018/inputParser')
 
-fs.readFile(filePath, { encoding: 'utf8' }, (err, data) => {
+fs.readFile(filePath, { encoding: 'utf8' }, (err, initData) => {
   if (err) throw err
 
-  data = inputToArray(data.trim())
-  // Manipulate input per puzzle instructions for Part 1
-  data[1] = 12
-  data[2] = 2
+  initData = inputToArray(initData.trim())
 
-  runProgram({ data })
-  const answer = data[0]
+  const resetInput = () => {
+    // Deep copy to ensure we aren't mutating the original data
+    return JSON.parse(JSON.stringify(initData))
+  }
+
+  const part1 = () => {
+    const data = resetInput()
+    // Manipulate input per puzzle instructions for Part 1
+    data[1] = 12
+    data[2] = 2
+    runProgram({ data })
+    return data[0]
+  }
+
+  const part2 = ({target, maxNoun, maxVerb}) => {
+
+    // Helper for running the program with specified noun and verb inputs
+    const tryProgram = ({
+      noun,
+      verb
+    }) => {
+      const data = resetInput()
+      data[1] = noun
+      data[2] = verb
+      runProgram({ data })
+      console.debug(`Running with noun:${noun} and verb:${verb} produces ${data[0]}`)
+      return Number(data[0])
+    }
+
+    // Manipulate and loop through attempts for Part 2
+    let noun = -1
+    while ( noun <= maxNoun) {
+      let verb = -1
+      noun++
+      while (verb <= maxVerb) {
+        verb++
+        output = tryProgram({
+          noun,
+          verb
+        })
+        // Break the search loop on success
+        if(output === target) {
+          return 100 * noun + verb
+        }
+      }
+    }
+  }
+
+
+  const answer1 = part1()
+  const answer2 = part2({ target:19690720, maxNoun: 99, maxVerb: 99})
 
   console.log('-- Part 1 --')
-  console.log(`Answer: ${answer}`)
+  console.log(`Answer: ${answer1}`)
+
+  console.log('-- Part 2 --')
+  console.log(`Answer: ${answer2}`)
 })