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feat: add Kaprekar number algorithm #1996

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feat: add Kaprekar number algorithm #1996

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26 changes: 26 additions & 0 deletions Maths/KaprekarNumber.js
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/**
* @function isKaprekarNumber
* @description A Kaprekar number is a positive integer whose square can
* be split into two parts that add up to the original number.
* For example, 9: 9²=81, 8+1=9. 45: 45²=2025, 20+25=45.
* @param {number} n - A positive integer
* @returns {boolean} - True if n is a Kaprekar number, false otherwise
* @see https://en.wikipedia.org/wiki/Kaprekar_number
* @example isKaprekarNumber(9) => true
* @example isKaprekarNumber(45) => true
* @example isKaprekarNumber(10) => false
*/
const isKaprekarNumber = (n) => {
if (!Number.isInteger(n) || n < 1) {
throw new TypeError('Input must be a positive integer')
}
const square = String(n * n)
for (let i = 1; i < square.length; i++) {
const left = Number(square.slice(0, i)) || 0
const right = Number(square.slice(i))
if (right > 0 && left + right === n) return true
}
return false
}

export { isKaprekarNumber }
51 changes: 51 additions & 0 deletions Maths/test/KaprekarNumber.test.js
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import { isKaprekarNumber } from '../KaprekarNumber.js'

describe('isKaprekarNumber', () => {
test('1 is NOT a Kaprekar number', () => {
expect(isKaprekarNumber(1)).toBe(false)
})

test('9 is a Kaprekar number (9²=81, 8+1=9)', () => {
expect(isKaprekarNumber(9)).toBe(true)
})

test('45 is a Kaprekar number (45²=2025, 20+25=45)', () => {
expect(isKaprekarNumber(45)).toBe(true)
})

test('55 is a Kaprekar number (55²=3025, 30+25=55)', () => {
expect(isKaprekarNumber(55)).toBe(true)
})

test('99 is a Kaprekar number (99²=9801, 98+01=99)', () => {
expect(isKaprekarNumber(99)).toBe(true)
})

test('297 is a Kaprekar number (297²=88209, 88+209=297)', () => {
expect(isKaprekarNumber(297)).toBe(true)
})

test('10 is NOT a Kaprekar number', () => {
expect(isKaprekarNumber(10)).toBe(false)
})

test('11 is NOT a Kaprekar number', () => {
expect(isKaprekarNumber(11)).toBe(false)
})

test('100 is NOT a Kaprekar number', () => {
expect(isKaprekarNumber(100)).toBe(false)
})

test('throws TypeError for zero', () => {
expect(() => isKaprekarNumber(0)).toThrow(TypeError)
})

test('throws TypeError for negative input', () => {
expect(() => isKaprekarNumber(-9)).toThrow(TypeError)
})

test('throws TypeError for float input', () => {
expect(() => isKaprekarNumber(9.5)).toThrow(TypeError)
})
})
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