developher-net · developher-net · Dec 7, 2020 · Dec 7, 2020 · Dec 7, 2020 · Dec 7, 2020
diff --git a/2020/day-03/airportRoute.js b/2020/day-03/airportRoute.js
@@ -0,0 +1,33 @@
+const queryPosition = ({ map, position }) => {
+  // check vertical position
+  const row = map.rows[position[1]]
+  // check horizontal which repeats
+  return row[(position[0] % row.length)]
+}
+
+const positionHasTree = ({ map, position }) => {
+  return (queryPosition({ map, position }) === '#')
+}
+
+const countTreesOnRoute = ({
+  map,
+  start = [0, 0],
+  slope = [3, 1]
+}) => {
+  let treeCount = 0
+  const position = start
+  const advance = () => {
+    position[0] += slope[0]
+    position[1] += slope[1]
+  }
+  while (position[1] < map.rows.length) {
+    if (positionHasTree({ map, position })) treeCount++
+    advance()
+  }
+  return treeCount
+}
+
+module.exports = {
+  countTreesOnRoute,
+  positionHasTree
+}
diff --git a/2020/day-03/airportRoute.test.js b/2020/day-03/airportRoute.test.js
@@ -0,0 +1,39 @@
+/* eslint-env mocha */
+const { expect } = require('chai')
+const { positionHasTree, countTreesOnRoute } = require('./airportRoute')
+const testData = [
+  '..##.......',
+  '#...#...#..',
+  '.#....#..#.',
+  '..#.#...#.#',
+  '.#...##..#.',
+  '..#.##.....',
+  '.#.#.#....#',
+  '.#........#',
+  '#.##...#...',
+  '#...##....#',
+  '.#..#...#.#'
+]
+
+describe('--- Day 3: Toboggan Trajectory ---', () => {
+  describe('Part 1', () => {
+    describe('positionHasTree()', () => {
+      it('can find a tree', () => {
+        expect(positionHasTree({ map: { rows: testData }, position: [4, 5] })).to.equal(true)
+        expect(positionHasTree({ map: { rows: testData }, position: [8, 9] })).to.equal(false)
+      })
+      it('can handle the horizontal terrain repeat', () => {
+        expect(positionHasTree({ map: { rows: testData }, position: [25, 5] })).to.equal(false)
+      })
+    })
+    describe('countTreesOnRoute()', () => {
+      it('tallies the number of trees on the route', () => {
+        expect(
+          countTreesOnRoute({
+            map: { rows: testData }
+          })
+        ).to.equal(7)
+      })
+    })
+  })
+})
diff --git a/2020/day-03/index.js b/2020/day-03/index.js
@@ -0,0 +1 @@
+require('./solution')