Day 11, part one

solutions/day11/solution.js

@@ -0,0 +1,73 @@
+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 () {
+  let input = (await read(fromHere('input.txt'), 'utf8')).trim().split('\n')
+  input = input.map(line => line.split(''))
+
+  await solveForFirstStar(input)
+  await solveForSecondStar(input)
+}
+
+function draw (input) {
+  for (const row of input) {
+    console.log(row.join(''))
+  }
+}
+
+function neighbors (input, row, col) {
+  let total = 0
+  if (input[row - 1]) {
+    if (input[row - 1][col - 1] === '#') total++
+    if (input[row - 1][col] === '#') total++
+    if (input[row - 1][col + 1] === '#') total++
+  }
+  if (input[row][col - 1] === '#') total++
+  if (input[row][col + 1] === '#') total++
+  if (input[row + 1]) {
+    if (input[row + 1][col - 1] === '#') total++
+    if (input[row + 1][col] === '#') total++
+    if (input[row + 1][col + 1] === '#') total++
+  }
+  return total
+}
+
+function step (input) {
+  const next = JSON.parse(JSON.stringify(input))
+  input.forEach((row, y, rows) => {
+    row.forEach((seat, x, seats) => {
+      if (seat === 'L' && neighbors(input, y, x) === 0) { next[y][x] = '#' }
+      if (seat === '#' && neighbors(input, y, x) >= 4) { next[y][x] = 'L' }
+    })
+  })
+  return next
+}
+
+function stabilize(input) {
+  // console.log('\nInput\n--------')
+  // draw(input)
+  let rounds = 1; let old; let fresh = input
+  do {
+    old = fresh
+    fresh = step(old)
+    // console.log(`\nRound ${rounds}\n--------`)
+    // draw(fresh)
+    rounds++
+  } while (JSON.stringify(old) !== JSON.stringify(fresh))
+  return fresh
+}
+
+async function solveForFirstStar (input) {
+  const stable = stabilize(input)
+  const filledSeats = stable.flat(2).filter(x => x=='#').length
+  report('Solution 1:', filledSeats)
+}
+
+async function solveForSecondStar (input) {
+  const solution = 'UNSOLVED'
+  report('Solution 2:', solution)
+}
+
+run()