8 - Medium - 奇偶链表

给定一个单链表，把所有的奇数节点和偶数节点分别排在一起。请注意，这里的奇数节点和偶数节点指的是节点编号的奇偶性，而不是节点的值的奇偶性。

请尝试使用原地算法完成。你的算法的空间复杂度应为 O(1)，时间复杂度应为 O(nodes)，nodes 为节点总数。

示例 1:

输入: 1->2->3->4->5->NULL
输出: 1->3->5->2->4->NULL
示例 2:

输入: 2->1->3->5->6->4->7->NULL
输出: 2->3->6->7->1->5->4->NULL
说明:

应当保持奇数节点和偶数节点的相对顺序。
链表的第一个节点视为奇数节点，第二个节点视为偶数节点，以此类推。

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def oddEvenList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head:
            return head
        odd = head
        if not head.next:
            return odd
        even = head.next
        even_head = even
        odd_tail = odd
        _continue = True
        while _continue:
            _continue = False
            if odd and odd.next:
                odd.next = odd.next.next
                odd_tail = odd
                odd = odd.next
                _continue = True
            if even and even.next:
                even.next = even.next.next
                even = even.next
                _continue = True
        if not odd:
            odd_tail.next = even_head
        else:
            odd.next = even_head
        return head

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def oddEvenList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        o = oddDummy = ListNode(-1)
        e = evenDummy = ListNode(-1)
        p = head
        isOdd = True
        while p:
            if isOdd:
                o.next = p
                o = o.next
                isOdd = False
            else:
                e.next = p
                e = e.next
                isOdd = True
            p = p.next
        o.next = evenDummy.next
        e.next = None
        return oddDummy.next