Quick Sort Template

def quickSort(self, nums):
        def helper(head, tail):
            if head >= tail: return 
            l, r = head, tail
            m = (r - l) // 2 + l
            pivot = nums[m]
            while r >= l:
                while r >= l and nums[l] < pivot: l += 1
                while r >= l and nums[r] > pivot: r -= 1
                if r >= l:
                    nums[l], nums[r] = nums[r], nums[l]
                    l += 1
                    r -= 1
            helper(head, r)
            helper(l, tail)

        helper(0, len(nums)-1)
        return nums