Ruby - Is A Number A Perfect Square?

Don’t rely on Math::sqrt.

It will let you down on very large numbers.

If you want to check if a very large number is a perfect square, find the nearest square with this binary search method. Then square the result and check if it matches your original number.

def approx_sqrt(num)
   low = 1
   high = num
   while high > low + 1
      mid = (high + low)/2
      if mid ** 2 <= num
         low = mid
      else
         high = mid
      end
   end
   return low
end