feat(2021-day-09): find the low points on the terrain

developher-net · developher-net · commit c445f4073839 · 2021-12-16T13:11:44.000-08:00
Solves part 1
diff --git a/2021/day-09/basins.js b/2021/day-09/basins.js
@@ -0,0 +1,44 @@
+const findLocalLows = (data) => {
+  const lows = []
+  const rows = data.split('\n')
+  let checked = 0
+
+  const isLow = (val, col, row) => {
+    // Collect points in each cardinal direction
+    const points = []
+    // TODO: If supporting diagonal checks, use this logic instead to loop
+    // for (let x = -1; x <= 1; x++) {
+    //   for (let y = -1; y <= 1; y++) {
+    //     if(x != 0 && y != 0)
+    //     if(rows[row + y] && rows[row + y][col + x]
+    //   }
+    // }
+    if (rows[row - 1] && rows[row - 1][col]) { points.push(parseInt(rows[row - 1][col])) }
+    if (rows[row + 1] && rows[row + 1][col]) { points.push(parseInt(rows[row + 1][col])) }
+    if (rows[row] && rows[row][col - 1]) { points.push(parseInt(rows[row][col - 1])) }
+    if (rows[row] && rows[row][col + 1]) { points.push(parseInt(rows[row][col + 1])) }
+
+    // NOTE - if the value is the same as a neighbor,
+    // that isn't counted as a low (even though together, they can be a low)
+    // ... this might be a concern for part 2 ....
+    return (val < Math.min(...points)) // value should be lower than any other points
+  }
+
+  rows.forEach((row, rowIdx) => {
+    for (let c = 0; c < row.length; c++) {
+      const cell = parseInt(row[c])
+      if (isLow(cell, c, rowIdx)) {
+        lows.push(cell)
+        console.debug(`Found low at ${c},${rowIdx}: ${cell}`)
+      }
+      checked++
+    }
+  })
+
+  console.debug(`Checked ${checked} cells`)
+  return lows
+}
+
+module.exports = {
+  findLocalLows
+}
diff --git a/2021/day-09/basins.test.js b/2021/day-09/basins.test.js
@@ -0,0 +1,24 @@
+/* eslint-env mocha */
+const { expect } = require('chai')
+const { findLocalLows } = require('./basins')
+
+const testData = `2199943210
+3987894921
+9856789892
+8767896789
+9899965678`
+
+describe.only('--- Day 9: Smoke Basin ---', () => {
+  describe('Part 1', () => {
+    describe('findLocalLows()', () => {
+      it('finds the local low points in the terrain', () => {
+        // low points in the testData are 1, 0 on row 0
+        // 5 on row 2
+        // 5 on row 5
+        const results = findLocalLows(testData)
+        expect(results.length).to.equal(4)
+        expect(results.reduce((a, b) => a + b)).to.equal(11)
+      })
+    })
+  })
+})
diff --git a/2021/day-09/index.js b/2021/day-09/index.js
@@ -0,0 +1,3 @@
+// eslint-disable-next-line no-unused-vars
+const console = require('../helpers')
+require('./solution')
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diff --git a/2021/day-09/solution.js b/2021/day-09/solution.js
@@ -0,0 +1,38 @@
+const fs = require('fs')
+const path = require('path')
+const filePath = path.join(__dirname, 'input.txt')
+const { linesToArray } = require('../../2018/inputParser')
+const { findLocalLows } = require('./basins')
+
+fs.readFile(filePath, { encoding: 'utf8' }, (err, initData) => {
+  if (err) throw err
+
+  initData = linesToArray(initData.trim())
+
+  const resetInput = () => {
+    // Deep copy to ensure we aren't mutating the original data
+    return JSON.parse(JSON.stringify(initData))
+  }
+
+  const part1 = () => {
+    const data = resetInput().join('\n')
+    const lows = findLocalLows(data)
+    console.debug(lows.length)
+    // risk profiles is the sum of each height + 1, which is the same as adding the count of lows
+    return lows.reduce((a, b) => a + b) + lows.length
+  }
+
+  const part2 = () => {
+    const data = resetInput()
+    // console.debug(data)
+    return 'No answer yet'
+  }
+  const answers = []
+  answers.push(part1())
+  answers.push(part2())
+
+  answers.forEach((ans, idx) => {
+    console.info(`-- Part ${idx + 1} --`)
+    console.info(`Answer: ${ans}`)
+  })
+})
diff --git a/index.js b/index.js
@@ -1 +1 @@
-require('./2021/day-08/solution')
+require('./2021/day-09/solution')

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+// eslint-disable-next-line no-unused-vars`
	`2`	`+const console = require('../helpers')`
	`3`	`+require('./solution')`
Original file line number	Diff line number	Diff line change
`@@ -1 +1 @@`
`1`		`-require('./2021/day-08/solution')`
	`1`	`+require('./2021/day-09/solution')`