------------
 Quick sort
------------

Sorts an array of values using quick sort;
https://en.wikipedia.org/wiki/Quick_sort

function quicksort(a, lo, hi)
	if lo < hi then
		local p=partition(a,lo,hi)
		quicksort(a,lo,p)
		quicksort(a,p+1,hi)
	end
end

function partition(a, lo, hi)
	local max=#collection
	local pivot=a[lo]
	local i=lo
	local j=hi
	while true do
		while a[i] < pivot do
			i=i+1
		end
		while a[j] > pivot do
			j=j-1
		end
		if (i>=j) return j
		swap(a,i,j)
	end
end