Day 9

solutions/day9/solution.js

@@ -0,0 +1,39 @@
+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(x => 1 * x)
+
+  const partOne = solveForFirstStar(input)
+  solveForSecondStar(partOne, input)
+}
+
+function solveForFirstStar (input) {
+  for (let i = 25; i < input.length; i++) {
+    const n = input[i]
+    const window = input.slice(i - 25, i)
+    if (window.filter(x => window.includes(n - x)).length === 0) {
+      report('Solution 1: ', n)
+      return n
+    }
+  }
+}
+
+function solveForSecondStar (partOne, input) {
+  for (let i = 0; i < input.length; i++) {
+    if (i < partOne) {
+      for (let t = 0, j = 0; t < partOne && i + j < input.length; j++) {
+        t += input[i + j]
+        if (t === partOne) {
+          const sequence = input.slice(i, i + j).sort((a, b) => a - b)
+          report('Solution 2:', sequence[0] + sequence[sequence.length - 1])
+          return
+        }
+      }
+    }
+  }
+}
+
+run()