Modified Kaprekar Numbers | Easy

A modified Kaprekar number is a positive whole number with a special property. If you square it, then split the number into two integers and sum those integers, you have the same value you started with. Consider a positive whole number n with d digits. We square n to arrive at a number that is either 2 X d digits long or (2 X d) - 1 digits long. Split the string representation of the square into two parts, l and r. The right hand part, r must be d digits long. The left is the remaining substring. Convert those two substrings back to integers, add them and see if you get n. For example, if n = 5, d = 1 then n^2 = 25. We split that into two strings and convert them back to integers 2 and 5. We test 2 + 5 != 5, so this is not a modified Kaprekar number. If n = 9, still d = 1 and n^2 = 81. This gives us 1 + 8 = 9, the original n.

Note: r nay have leading zeros.

Here’s an explanation from Wikipedia about the ORIGINAL Kaprekar Number (spot the difference!):

In mathematics, a Kaprekar number for a given base is a non-negative integer, the representation of whose square in that base can be split into two parts that add up to the original number again. For instance, 45 is a Kaprekar number, because 45² = 2025 and 20+25 = 45.

Given two positive integers p and q where p is lower than q, write a program to print the modified Kaprekar numbers in the range between p and q, inclusive.

Function Description

Complete the kaprekarNumbers function in the editor below. It should print the list of modified Kaprekar numbers in ascending order.

kaprekarNumbers has the following parameter(s):

• p: an integer
• q: an integer

Input Format

The first line contains the lower integer limit p. The second line contains the upper integer limit q.

Note: Your range should be inclusive of the limits.

Output Format

Output each modified Kaprekar number in the given range, space-separated on a single line. If no modified Kaprekar numbers exist in the given range, print INVALID RANGE.

Sample Input

1
100

Sample Output

1 9 45 55 99

My Solution

function kaprekarNumbers(p, q) {
  const result = [...Array(q - p + 1)].reduce((a, _, i) => {
    const number = p + i
    const sqrt = (number * number).toString()

    if (number < 2) return number

    const floor = Math.floor(sqrt.length / 2)

    const [front, rear] = [
      sqrt.substr(0, floor),
      sqrt.substr(floor, sqrt.length)
    ]

    if ((+front + +rear) === number) return a + (!a ? number : ` ${number}`)

    return a
  }, '')

  return result || 'INVALID RANGE'
}

const r1 = kaprekarNumbers(1, 100)
console.log(`실행 결과: ${r1}, 기대값: 1 9 45 55 99`)
const r2 = kaprekarNumbers(100, 300)
console.log(`실행 결과: ${r2}, 기대값: 297`)