#README
#Run by typing "ruby (filename)".  Drive code is already included.
#This script adds a method "find_pivot" to the array class which finds the pivot point of any array
#and returns the index of that point if it exists or -1 otherwise.

class Array
	def find_pivot
		raise NoMethodError, 'Wrong type of input!' if self.class != Array
		
		low = 0
		high = self.length - 1
		mid = (low + high) / 2
		searches = 0

		until searches == (self.length / 2)
			searches += 1
			left_sum = self[low..mid - 1].inject {|sum, i| sum + i}
			right_sum = self[mid + 1..high].inject{|sum, i| sum + i}

			if left_sum == right_sum
				return mid
			elsif right_sum > left_sum
				mid += 1
			elsif left_sum > right_sum
				mid -= 1
			end
		end
		return -1
	end
end

p "[1,4,6,3,2].find_pivot yields " + "#{[1,4,6,3,2].find_pivot}."
p "[1,4,6,7,3,2].find_pivot yields " + "#{[1,4,6,7,3,2].find_pivot}."