Find square root using Newton's Method -- Ruby version (we use a trick to get a good starting seed value)

sqrt.rb

# https://www.codewars.com/kata/square-root-without-using-library-math

# the challenge stipulates:  don't require any libs, don't use ** operator (exponentiation)
# the challenge also says all inputs will already be perfect squares of integers
# This code works for very large integers as well as small ones

def square_root_me(num)
  start = num.to_s(2); start = start[0,(start.length/2)].to_i(2)
  retval = start
  for i in 0..10000 do
    # (Note: i is not used; we want to avoid an infinite loop if we're given bad input)
    retval = ((retval + num/retval)/2).to_i
    return retval if retval*retval == num
  end
end