feat(2021-day-10): find incomplete line errors

solves part 2

2021/day-10/linting.js

@@ -30,21 +30,25 @@ const lintLine = (line) => {
     pos++
   }
 
-  // if we run out of line, ignore per instructions for Step 1
+  // if we run out of characters in the line, that means it is
+  // incomplete, and we need to provide an autocomplete suggestion
   if (expected.length > 0) {
-    // TODO - add the reporting when we need it in Step 2?
+    // Reversing the 'expected' string gives us the autocomplete suggestion
+    return {
+      suggestion: [...expected].reverse().join('')
+    }
   }
 }
 
 const lintAll = (instructions) => {
   const errors = instructions.map(lintLine) // lint each line
     .map((error, idx) => {
       return { ...error, line: idx }
-    }).filter((report) => !!(report.char)) // remove lines without errors
+    }).filter((report) => !!(report.char) || !!(report.suggestion)) // remove lines without errors
 
   console.log(`Linting found ${errors.length} errors in ${instructions.length} lines.`)
-  console.debug(instructions)
-  console.debug(errors)
+  // console.debug(instructions)
+  // console.debug(errors)
 
   return errors
 }

2021/day-10/linting.test.js

@@ -20,6 +20,14 @@ const testData = `[({(<(())[]>[[{[]{<()<>>
 <{([([[(<>()){}]>(<<{{
 <{([{{}}[<[[[<>{}]]]>[]]`
 
+const autocomplete = {
+  '[({(<(())[]>[[{[]{<()<>>': '}}]])})]',
+  '[(()[<>])]({[<{<<[]>>(': ')}>]})',
+  '(((({<>}<{<{<>}{[]{[]{}': '}}>}>))))',
+  '{<[[]]>}<{[{[{[]{()[[[]': ']]}}]}]}>',
+  '<{([{{}}[<[[[<>{}]]]>[]]': '])}>'
+}
+
 describe('--- Day 10: Syntax Scoring ---', () => {
   describe('Part 1', () => {
     describe('lintLine()', () => {
@@ -57,6 +65,7 @@ describe('--- Day 10: Syntax Scoring ---', () => {
     describe('lintAll', () => {
       it('finds all lines with linting errors', () => {
         const errors = lintAll(testData.split('\n'))
+          .filter((err) => (err.char))
 
         expect(errors.length).to.equal(5)
         expect(errors[0]).to.deep.equal({
@@ -90,6 +99,25 @@ describe('--- Day 10: Syntax Scoring ---', () => {
           found: '>'
         })
       })
+      it('provides autocomplete suggestions for incomplete lines', () => {
+        const data = testData.split('\n')
+        const errors = lintAll(data)
+          .filter((err) => !!err.suggestion)
+
+        expect(errors.length).to.equal(5)
+        errors.forEach((err) => {
+          expect(err.suggestion).to.equal(
+            autocomplete[data[err.line]]
+          )
+        })
+      })
+      it('skips lines without errors', () => {
+        const errors = lintAll([
+          '[]',
+          '[()]'
+        ])
+        expect(errors.length).to.equal(0)
+      })
     })
   })
 })

2021/day-10/solution.js

@@ -3,6 +3,7 @@ const path = require('path')
 const filePath = path.join(__dirname, 'input.txt')
 const { linesToArray } = require('../../2018/inputParser')
 const { lintAll } = require('./linting')
+const { scoreAutocomplete, findMiddleScore } = require('./scoring')
 
 fs.readFile(filePath, { encoding: 'utf8' }, (err, initData) => {
   if (err) throw err
@@ -25,13 +26,19 @@ fs.readFile(filePath, { encoding: 'utf8' }, (err, initData) => {
 
     const errors = lintAll(data)
 
-    return errors.reduce((total, error) => total + points[error.found], 0)
+    // Score the premature closure errors
+    return errors.filter((err) => !!err.char)
+      .reduce((total, error) => total + points[error.found], 0)
   }
 
   const part2 = () => {
     const data = resetInput()
-    console.debug(data)
-    return 'No answer yet'
+    // find the incomplete line errors
+    const errors = lintAll(data).filter((err) => !!err.suggestion)
+
+    const scores = errors.map((err) => scoreAutocomplete(err.suggestion))
+
+    return findMiddleScore(scores)
   }
   const answers = []
   answers.push(part1())