Merge pull request #121 from amclin/feat/prep-2020

Solution for 2020 Day 1 parts 1 and 2

2020/day-01/expenseValidation.js

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+
+/**
+ * Validates a list of records by comparing every combination
+ * to the checksum. Stops when the first match is found
+ * @param {array} records List of records to check
+ * @param {int} checksum The target sum that records should add up to
+ * @param {int} goal The number of records we hope to find
+ */
+const validateRecords = (records, checksum = 2020, goal = 2) => {
+  const results = []
+
+  // Intentionally using `function()` instead of `() =>` because
+  // the thisArg won't get passed to the find callback otherwise
+  // https://stackoverflow.com/questions/46639131/javascript-array-prototype-find-second-argument-thisarg-not-working
+  function matcher (record) {
+    this.depth = this.depth || 1 // depth tracking starts at level 1
+    this.tracker = this.tracker || 0 // for basic sums, start counter at 0
+    const subTotal = this.tracker + record
+    // Found a match in the specified with desired qty of results, don't keep searching!
+    if (subTotal === this.target && this.depth >= goal) {
+      results.push(record)
+      return true
+    }
+    // When subtotal exceeds target, return immediately and don't waste time
+    // on more loops that won't get results
+    if (subTotal > this.target) {
+      return false
+    }
+    // If we're already at max depth, don't waste time on more loops
+    if (this.depth >= this.maxDepth) {
+      return false
+    }
+    // Check the next level down
+    const res = records.find(matcher, {
+      maxDepth: this.maxDepth,
+      target: this.target,
+      depth: this.depth + 1,
+      tracker: this.tracker + record
+    })
+    // Propogate maches back up the recursion chain, capturing each
+    if (res) {
+      results.push(record)
+      return true
+    }
+    // Nothing found with this combo, step to the next sibling
+    return false
+  }
+
+  // Parse the records to find results
+  records.find(matcher, {
+    maxDepth: goal,
+    target: checksum
+  })
+
+  if (results.length < 2) {
+    throw new Error('Couldn\'t find a checksum match')
+  }
+  return results
+}
+
+module.exports = {
+  validateRecords
+}

2020/day-01/expenseValidation.test.js

@@ -0,0 +1,78 @@
+/* eslint-env mocha */
+const { expect } = require('chai')
+const { validateRecords } = require('./expenseValidation')
+
+/**
+ * Sum all the values in an array
+ */
+const arrSum = (arr) => arr.reduce((x, y) => x + y, 0)
+/**
+ * Multiply all the values in an array
+ */
+const arrMult = (arr) => arr.reduce((x, y) => x * y, 1)
+const testData = [
+  1721,
+  979,
+  366,
+  299,
+  675,
+  1456
+]
+
+describe('--- 2020 Day 1: Report Repair ---', () => {
+  describe('Part 1', () => {
+    describe('validateRecords()', () => {
+      it('it finds the two records that sum to 2020', () => {
+        const expected = [1721, 299]
+        const results = validateRecords(testData, undefined, 2)
+        // Should be 2 results
+        expect(results.length).to.equal(2)
+        // Result order is unnecessary, but all expected hould be in the result set
+        expected.forEach(result => {
+          expect(testData.indexOf(result)).to.be.greaterThan(-1)
+        })
+        // Results add up to the checksum
+        expect(arrSum(results)).to.equal(2020)
+        // Confirm the multiplied total
+        expect(arrMult(results)).to.equal(514579)
+      })
+      it('it supports specifying an alternate checksum', () => {
+        const expected = [testData[3], testData[5]]
+        const checksum = arrSum(expected)
+        const results = validateRecords(testData, checksum)
+        // Should be 2 results
+        expect(results.length).to.equal(2)
+        // Result order is unnecessary, but all expected hould be in the result set
+        expected.forEach(result => {
+          expect(results.indexOf(result)).to.be.greaterThan(-1)
+        })
+        // Results add up to the checksum
+        expect(arrSum(results)).to.equal(checksum)
+      })
+      it('Throws an error when no records provided', () => {
+        expect(validateRecords).to.throw()
+      })
+      it('Throws an error when no records match checksum', () => {
+        expect(() => validateRecords([1, 2, 3], 100)).to.throw('Couldn\'t find a checksum match')
+      })
+    })
+  })
+  describe('Part 2', () => {
+    describe('validateRecords()', () => {
+      it('it can find a specified number of records adding up to 2020', () => {
+        const expected = [979, 366, 675]
+        const results = validateRecords(testData, undefined, 3)
+        // Should same number of results
+        expect(results.length).to.equal(expected.length)
+        // Result order is unnecessary, but all expected hould be in the result set
+        expected.forEach(result => {
+          expect(testData.indexOf(result)).to.be.greaterThan(-1)
+        })
+        // Results add up to the checksum
+        expect(arrSum(results)).to.equal(2020)
+        // Confirm the multiplied total
+        expect(arrMult(results)).to.equal(241861950)
+      })
+    })
+  })
+})

2020/day-01/index.js

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+require('./solution')

2020/day-01/input.txt

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+1539
+1914
+1866
+1407
+1706
+1423
+1834
+1700
+1573
+1486
+1743
+1394
+1693
+1705
+1530
+1811
+1626
+1473
+1901
+1481
+1527
+1841
+1891
+1750
+1343
+1899
+401
+1896
+1627
+1593
+1541
+874
+1484
+1210
+1692
+1963
+1964
+1780
+671
+1862
+1393
+1309
+1740
+1831
+1932
+1185
+1979
+1504
+1663
+1610
+1494
+1511
+1103
+1738
+1816
+1871
+1545
+1595
+1784
+1412
+1815
+1998
+1783
+1770
+1426
+1699
+1416
+1880
+1612
+1989
+1360
+1869
+1762
+1690
+1999
+1990
+1521
+1730
+703
+1463
+1670
+1472
+1413
+1669
+1502
+1548
+1475
+1694
+1314
+1980
+980
+1667
+890
+1569
+1456
+1406
+1924
+1973
+1965
+1533
+1827
+2000
+1847
+1520
+1729
+1512
+1555
+1566
+1505
+1672
+1169
+1835
+1850
+1493
+1861
+1288
+1675
+1676
+1556
+1320
+1757
+1870
+1642
+1903
+1372
+1967
+1894
+176
+1908
+1418
+1535
+1487
+1496
+1491
+1611
+1970
+1758
+1563
+1766
+1629
+1937
+1763
+1829
+1772
+1632
+1517
+1736
+1971
+1721
+1716
+1429
+1408
+1560
+1958
+1359
+1890
+1825
+1536
+1819
+1697
+1887
+1832
+2005
+892
+1471
+1425
+1677
+1673
+1128
+1878
+1062
+1470
+1875
+1854
+1518
+1568
+1919
+256
+1532
+1711
+1944
+1344
+1330
+1636
+1957
+1709
+1551
+1983
+1674
+1671
+1959
+1760
+1689
+1767
+1477
+1589
+1897
+1144
+1982
+1544

2020/day-01/solution.js

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+const fs = require('fs')
+const path = require('path')
+const filePath = path.join(__dirname, 'input.txt')
+const { validateRecords } = require('./expenseValidation')
+const { inputToArray } = require('../../2018/inputParser')
+
+fs.readFile(filePath, { encoding: 'utf8' }, (err, initData) => {
+  if (err) throw err
+
+  initData = inputToArray(initData.trim())
+    .map(el => Number(el))
+
+  const resetInput = () => {
+    // Deep copy to ensure we aren't mutating the original data
+    return JSON.parse(JSON.stringify(initData))
+  }
+
+  const part1 = () => {
+    const data = resetInput()
+    return validateRecords(data) // Find 2 results for 2020
+      .reduce((total, res) => total * res, 1)
+  }
+
+  const part2 = () => {
+    const data = resetInput()
+    return validateRecords(data, undefined, 3) // Find 3 results for 2020
+      .reduce((total, res) => total * res, 1)
+  }
+  const answers = []
+  answers.push(part1())
+  answers.push(part2())
+
+  answers.forEach((ans, idx) => {
+    console.info(`-- Part ${idx + 1} --`)
+    console.info(`Answer: ${ans}`)
+  })
+})