Day 10

solutions/day10/solution.js

@@ -0,0 +1,48 @@
+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).sort((a, b) => b - a)
+  input.push(0)
+  input.unshift(input[0] + 3)
+
+  solveForFirstStar(input)
+  solveForSecondStar(input)
+}
+
+function solveForFirstStar (input) {
+  let ones = 0
+  let threes = 0
+  input.forEach((s, i, S) => {
+    const diff = s - S[i + 1]
+    if (diff === 1) {
+      ones++
+    }
+    if (diff === 3) {
+      threes++
+    }
+  })
+  const solution = ones * threes
+  report('Solution 1:', solution)
+}
+
+function solveForSecondStar (input) {
+  const choices = []
+  input.forEach((s, i, S) => {
+    choices[i] = i === 0 ? 1 : 0
+    for (let j = 1; ; j++) {
+      if (S[i - j] - s <= 3) {
+        choices[i] += choices[i - j]
+      } else {
+        break
+      }
+    }
+  })
+
+  const solution = choices[choices.length - 1]
+  report('Solution 2:', solution)
+}
+
+run()