Day 1 solved

solutions/day1/solution.js

@@ -0,0 +1,45 @@
+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 => parseInt(x, 10))
+
+  await solveForFirstStar(input)
+  await solveForSecondStar(input)
+}
+
+function findSum (array, startIndex, sum, count = 2) {
+  for (let i = 0; i < array.length; i++) {
+    const n = array[i]
+    if (count > 2) {
+      const searchResult = findSum(array, i + 1, sum - n, count - 1)
+      if (searchResult) {
+        return [n, ...searchResult]
+      }
+    } else if (count === 2) {
+      for (let j = startIndex + 1; j < array.length; j++) {
+        if (n + array[j] === sum) {
+          return [n, array[j]]
+        }
+      }
+    } else {
+      throw new Error('findSum: Invalid count')
+    }
+  }
+  return null
+}
+
+async function solveForFirstStar (input) {
+  const solution = findSum(input, 0, 2020, 2).reduce((acc, cur) => acc * cur, 1)
+  report('Input:', input)
+  report('Solution 1:', solution)
+}
+
+async function solveForSecondStar (input) {
+  const solution = findSum(input, 0, 2020, 3).reduce((acc, cur) => acc * cur, 1)
+  report('Solution 2:', solution)
+}
+
+run()