Day 2 solved

solutions/day2/solution.js

@@ -0,0 +1,50 @@
+const path = require('path')
+const { read, position } = require('promise-path')
+const fromHere = position(__dirname)
+const report = (...messages) => console.log(`[${require(fromHere('../../package.json')).logName} / ${__dirname.split(path.sep).pop()}]`, ...messages)
+
+function mapInput (line) {
+  const regex = /(?<num1>[0-9]+)-(?<num2>[0-9]+) (?<letter>[a-z]): (?<password>.+)$/
+  return line.match(regex).groups
+}
+
+function XOR (a, b) {
+  return a ? !b : !!b
+}
+
+async function run () {
+  const input = (await read(fromHere('input.txt'), 'utf8')).trim().split('\n').map(mapInput)
+
+  await solveForFirstStar(input)
+  await solveForSecondStar(input)
+}
+
+async function solveForFirstStar (input) {
+  const solution = input.filter(
+    ({ num1, num2, letter, password }) => {
+      let count = 0
+      for (let i = 0; i < password.length; i++) {
+        if (password.charAt(i) === letter) {
+          count++
+          if (count > num2) {
+            return false
+          }
+        }
+      }
+      return count >= num1
+    }
+  ).length
+  report('Input:', input)
+  report('Solution 1:', solution)
+}
+
+async function solveForSecondStar (input) {
+  const solution = input.filter(
+    ({ num1, num2, letter, password }) => {
+      return XOR(password.charAt(num1 - 1) === letter, password.charAt(num2 - 1) === letter)
+    }
+  ).length
+  report('Solution 2:', solution)
+}
+
+run()