RAVI

ravi.rb

def find_ravi_pairs_in_bound(n)
  ravis = []
  # Just setting an upper bound on this for now
  (1..(n/2)).each do |i|
    (i..n).each do |j|
      # Add the two numbers together and convert them to binary string
      a = (i + j).to_s(2)
      # Multiply the two numbers together and convert them to binary string
      b = (i * j).to_s(2).reverse
      # just working with the upper bound
      break if i * j > n
      # the reversed string b could have a bunch of leading zeros which
      # would not be present in a. We trim these zeros so we can compare
      # (leading zeros in a binary string don't matter)
      b = trim_zeros(b)
      if a == b
        # We found a pair, add them to the array
        ravis.push([i, j]) if a == b
      end
    end
  end
  return ravis
end

# Removes leading zeros from a binary string
def trim_zeros(bin_string)
  # Get the index of the first one
  zero_pad_index = bin_string.index('1')
  # remove all the zeros up to the leading one
  return bin_string.slice(zero_pad_index, bin_string.length)
end