Day 8

solutions/day8/solution.js

@@ -0,0 +1,55 @@
+const path = require('path')
+const { read, position } = require('promise-path')
+const fromHere = position(__dirname)
+const report = (...messages) => console.log(`[${require(fromHere('../../package.json')).logName} / ${__dirname.split(path.sep).pop()}]`, ...messages)
+
+async function run () {
+  const input = (await read(fromHere('input.txt'), 'utf8')).trim().split('\n').map(l => /(\w+) (.+)/.exec(l).slice(1))
+
+  await solveForFirstStar(input)
+  await solveForSecondStar(input)
+}
+
+function execute (input) {
+  let pointer = 0; let accumulator = 0
+  let clean = true
+  const counts = Array(input.length).fill(0)
+  const ops = {
+    nop: () => { pointer++ },
+    acc: x => { accumulator += x; pointer++ },
+    jmp: x => { pointer += x }
+  }
+  while (pointer < input.length) {
+    const [op, x] = input[pointer]
+    counts[pointer]++
+    if (counts.includes(2)) {
+      clean = false
+      break
+    }
+    ops[op](1 * x)
+  }
+  return { accumulator, clean }
+}
+
+function solveForFirstStar (input) {
+  report('Solution 1:', execute(input).accumulator)
+}
+
+async function solveForSecondStar (input) {
+  const swaps = []
+  input.forEach(([op, offset], index) => {
+    if (op === 'nop' || op === 'jmp') {
+      const swap = input.slice()
+      swap[index] = [op === 'nop' ? 'jmp' : 'nop', offset]
+      swaps.push(swap)
+    }
+  })
+  for (const swap of swaps) {
+    const result = execute(swap)
+    if (result.clean) {
+      report('Solution 2:', result.accumulator)
+    }
+  }
+}
+
+run()