Rosetta Code

Kaprekar numbers

Test fixed integers for the Kaprekar split-square property.

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Sourcerosettacode/popular/kaprekar_numbers.vibe
def digit_value(char: string) -> int
  digit = "0123456789".index(char)
  raise ArgumentError, "expected a decimal digit" if digit == nil
  digit
end

def to_int(text: string) -> int
  if text == ""
    return 0
  end

  value = 0
  index = 0
  while index < text.length
    value = (value * 10) + digit_value(text.chars.fetch(index))
    index = index + 1
  end
  value
end

def kaprekar?(number: int) -> bool
  if number == 1
    return true
  end

  square = (number * number).to_s
  split = 1

  while split < square.length
    left = to_int(square.chars.first(split).join)
    right = to_int(square.chars.drop(split).join)
    if right != 0 && left + right == number
      return true
    end
    split = split + 1
  end

  false
end

def run -> array<{ kaprekar: bool, value: int }>
  [
    { value: 1, kaprekar: kaprekar?(1) },
    { value: 45, kaprekar: kaprekar?(45) },
    { value: 55, kaprekar: kaprekar?(55) },
    { value: 99, kaprekar: kaprekar?(99) },
    { value: 297, kaprekar: kaprekar?(297) },
    { value: 703, kaprekar: kaprekar?(703) },
    { value: 10, kaprekar: kaprekar?(10) }
  ]
end

Output

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