merge_sort_inversions

a = []

#the following inputs the test file and puts it into array a when IntegerArray is the input
File.open("IntegerArray.txt").each_line do |line|
	a << line.to_i
end

$inversion_count = 0

def merge_sort(array)
	return array if array.length == 1

	left, right, array = array.shift((array.length/2).round), array, []
	
	left, right = merge_sort(left), merge_sort(right)

	while !left.empty? and !right.empty?
		if left.first < right.first
			array<<left.shift
		else
			$inversion_count += left.length
			array<<right.shift
		end
	end
	array + left + right
end

puts merge_sort(a)
print $inversion_count