题解 | #链表的奇偶重排#

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param head ListNode类 
# @return ListNode类
#
class Solution:
    def oddEvenList(self , head: ListNode) -> ListNode:
        if head is None:
            return None
        flag = 'odd' #初始化奇偶标志为“奇”，第一个计数下标是奇数
        oddlist = ListNode(-1)
        oddcur = oddlist
        evenlist = ListNode(-1)
        evencur = evenlist
        while head: #按标志分别添加进奇偶链表
            if flag == 'odd':
                newNode = ListNode(head.val)
                oddcur.next = newNode
                oddcur = oddcur.next
                flag = 'even'
            elif flag == 'even':
                newNode = ListNode(head.val)
                evencur.next = newNode
                evencur = evencur.next
                flag = 'odd'
            head = head.next
        oddcur.next = evenlist.next #奇链表连接偶链表
        return oddlist.next