Odd Even Linked List

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def oddEvenList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if head == None:
            return head

        oddEnd, evenEnd, evenHead = head, head.next, head.next
        while evenEnd != None and evenEnd.next != None:
            oddEnd.next, evenEnd.next  = evenEnd.next, evenEnd.next.next
            oddEnd, evenEnd = oddEnd.next, evenEnd.next
        oddEnd.next = evenHead
        return head