solutions 133

1 files changed, 105 insertions, 0 deletions

diff --git a/challenge-133/iangoodnight/javascript/ch-2.js b/challenge-133/iangoodnight/javascript/ch-2.js
new file mode 100755
index 0000000000..5f229008ec
--- /dev/null
+++ b/challenge-133/iangoodnight/javascript/ch-2.js
@@ -0,0 +1,105 @@
+#!/usr/bin/env node
+// ch-2.js
+
+/**
+ * https://theweeklychallenge.org/blog/perl-weekly-challenge-133/
+ *
+ * Task 2 > Smith Numbers
+ * ======================
+ *
+ * Write a script to generate the first 10 `Smith Numbers` in base 10.
+ *
+ * According to Wikipedia:
+ *
+ * > In number theory, a Smith number is a composite number for which, in a
+ * > given number base, the sum of its digits is equal to the sum of the digits
+ * > in its prime factorization in the given number base.
+ *
+ **/
+
+'use strict';
+
+/**
+ * Our PWC solution and some helper functions
+ **/
+
+// First, we need a utility function to return our prime factors
+function primeFactors(number) {
+  let n = parseInt(number, 10); // Input validation
+  if (number === 'NaN') {
+    // Fail fast if arg is not a positive integer
+    throw new Error(
+      'function `primeFactors` expects a positive integer as an argument.',
+    );
+  }
+  const factors = [];
+
+  let divisor = 2; // Starting with 2, check for remainder
+  while (n >= 2) {
+    if (n % divisor === 0) {
+      // If modulo is 0, push to factors
+      factors.push(divisor);
+      n /= divisor;
+    } else {
+      divisor += 1; // Else, increment the divisor and try again
+    }
+  }
+  return factors;
+}
+
+// Reduce numbers to the sum of their digits
+function sumDigits(number) {
+  return number
+    .toString()
+    .split('')
+    .reduce((sum, digit) => sum + parseInt(digit, 10), 0);
+}
+
+// Find our actual smith numbers with the help of `primeFactors` and `sumDigits`
+function identifySmithNumbers(limit = 10) {
+  const smithNumbers = [];
+
+  let test = 4; // Smith numbers are composite numbers, so skip the primes
+  while (smithNumbers.length < limit) {
+    const primeFactorsArr = primeFactors(test);
+
+    const factorSum = primeFactorsArr.reduce(
+      (sum, factor) => sum + sumDigits(factor),
+      0,
+    );
+
+    const digitSum = sumDigits(test);
+
+    if (factorSum === digitSum && primeFactorsArr.length !== 1) {
+      smithNumbers.push(test);
+    }
+    test += 1;
+  }
+  return smithNumbers;
+}
+
+/**
+ * General utilities
+ **/
+
+// Takes an array and returns it as human-readable comma separated list
+function stringWithOxfordComma(arr = []) {
+  const reversed = [...arr].reverse();
+
+  const [last, ...rest] = reversed;
+
+  const first = [...rest].reverse().join(', ');
+
+  return `${first}, and ${last}`;
+}
+
+// IIFE to handle args and print results
+(function main() {
+  const limit = process.argv[2] || 10;
+
+  const smithNumbers = identifySmithNumbers(limit);
+
+  const stringified = stringWithOxfordComma(smithNumbers);
+
+  console.log(`The first ${limit} Smith Numbers are ${stringified}.`);
+})();