Method split

leetcode/143. Reorder List.py:26–35

(self, head)

        head = self.reConnect(ahead, behind)
    # split the linkedlist in middle
    def split(self, head):
        fast = head
        slow = head
        while fast and fast.next:
            slow = slow.next
            fast = fast.next
            fast = fast.next
        middle = slow.next
        slow.next = None
        return head, middle
    # reverse the behind half linkedlist
    def reverse(self, head):
        reHead = None