Binary search

binary_search.rb

def binary_search(list, item)
  low = 0
  high = list.size - 1
  
  return nil if list.last < item # item not in array
  
  while low < high do
  	mid = (low + high) / 2
  	guess = list[mid]
  	
  	if guess == item
  		return mid
  	elsif guess > item
  	  high = mid - 1
  	else
  	  high = mid + 1
  	end
  end
  
  # while terminated without finding anything
  return nil
end

p binary_search([1,3,4,6,100], 4)
p binary_search([1,3,4,6,100], 400)
p binary_search(['f', 'g', 'h', 'i'], 'h')
p binary_search(['fa', 'ga', 'ha', 'ia'], 'ia')