Day 7

solutions/day7/solution.js

@@ -0,0 +1,78 @@
+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 () {
+  // light red bags contain 1 bright white bag, 2 muted yellow bags.
+  const input = (await read(fromHere('input.txt'), 'utf8')).trim().split('\n').map(
+    line => {
+      const [color, rest] = line.split(' bags contain ')
+      let contents
+      if (rest === 'no other bags.') contents = []
+      else {
+        contents = rest.slice(0, -1).split(', ').map(i => {
+          const [, qty, color] = i.match(/(\d+) (.+) bags?/)
+          return {
+            quantity: 1 * qty,
+            color
+          }
+        })
+      }
+      return {
+        color,
+        contents
+      }
+    }
+  ).reduce((acc, cur) => ({ ...acc, [cur.color]: cur.contents }), {})
+  /*
+{
+  color
+  contents: [
+    { quantity, color}
+  ]
+}
+*/
+
+  await solveForFirstStar(input)
+  await solveForSecondStar(input)
+}
+
+async function solveForFirstStar (input) {
+  const outerColors = new Set()
+  Object.entries(input).forEach(([color, contents]) => {
+    if (contents.some(
+      bag => bag.color === 'shiny gold')
+    ) {
+      outerColors.add(color)
+    }
+  })
+  let oldSize
+  while (oldSize !== outerColors.size) {
+    oldSize = outerColors.size
+    Object.entries(input).forEach(
+      ([color, contents]) => {
+        if (
+          !outerColors.has(color) &&
+          contents.some(bag => outerColors.has(bag.color))
+        ) {
+          outerColors.add(color)
+        }
+      }
+    )
+  }
+  const solution = outerColors.size
+  //  report('Input:', input);
+  report('Solution 1:', solution)
+}
+
+function count (input, color) {
+  if (input[color].length === 0) return 1
+  return input[color].reduce((acc, bag) => acc + bag.quantity * count(input, bag.color), 1)
+}
+
+async function solveForSecondStar (input) {
+  report('Solution 2:', count(input, 'shiny gold') - 1)
+}
+
+run()