Rosetta Code

Long multiplication

Break a multiplication problem into the partial products used by long multiplication.

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

def power_of_ten(exponent: int) -> int
  value = 1
  count = 0

  while count < exponent
    value = value * 10
    count = count + 1
  end

  value
end

def partial_products(multiplicand: int, multiplier: int) -> array<int>
  digits = multiplier.to_s
  products: array<int> = []
  shift = 0
  index = digits.length - 1

  while index >= 0
    products.push(multiplicand * digit_value(digits.chars.fetch(index)) * power_of_ten(shift))
    shift = shift + 1
    index = index - 1
  end

  products
end

def run -> { multiplicand: int, multiplier: int, partials: array<int>, product: int }
  multiplicand = 123
  multiplier = 45
  {
    multiplicand: multiplicand,
    multiplier: multiplier,
    partials: partial_products(multiplicand, multiplier),
    product: multiplicand * multiplier
  }
end

Output

Click Run example to see the result.

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