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Added a new Maths algorithm to determine if two non-null integers are "friendly numbers" #1267

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raklaptudirm merged 3 commits into TheAlgorithms:master from fun-guava:friendly_numbers
Nov 30, 2022
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41 changes: 41 additions & 0 deletions Maths/FriendlyNumbers.js
View file Open in desktop
Original file line number Diff line number Diff line change
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/*
'In number theory, friendly numbers are two or more natural numbers with a common abundancy index, the
ratio between the sum of divisors of a number and the number itself.'
Source: https://en.wikipedia.org/wiki/Friendly_number
See also: https://mathworld.wolfram.com/FriendlyNumber.html#:~:text=The%20numbers%20known%20to%20be,numbers%20have%20a%20positive%20density.
*/

export const FriendlyNumbers = (firstNumber, secondNumber) => {
// input: two integers
// output: true if the two integers are friendly numbers, false if they are not friendly numbers

// First, check that the parameters are valid
if (!Number.isInteger(firstNumber) || !Number.isInteger(secondNumber) || firstNumber === 0 || secondNumber === 0 || firstNumber === secondNumber) {
throw new Error('The two parameters must be distinct, non-null integers')
}

// Calculate the abundancy index of the two number.
// ... first get the sum of their divisors
let sumDivisorsFirstNumber = firstNumber
let sumDivisorsSecondNumber = secondNumber

for (let i = 0; i < firstNumber / 2; i++) {
if (Number.isInteger(firstNumber / i)) {
sumDivisorsFirstNumber += i
}
}
for (let i = 0; i < secondNumber / 2; i++) {
if (Number.isInteger(secondNumber / i)) {
sumDivisorsSecondNumber += i
}
}
// ... and divide that sum by the number itself
const abundancyIndexFirstNumber = sumDivisorsFirstNumber / firstNumber
const abundancyIndexSecondNumber = sumDivisorsSecondNumber / secondNumber

if (abundancyIndexFirstNumber === abundancyIndexSecondNumber) {
return true
} else {
return false
}
}

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