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#!/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}.`);
})();
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