记录奇偶位置，交换奇偶值即可。
# Definition for singly-linked list. # class ListNode: # def __init__(self, x): # self.val = x # self.next = None class Solution: def swapPairs(self, head: ListNode) -> ListNode: result = ListNode(0) r = result cnt = 0 tmp_val = "None" while head: cnt += 1 if cnt %2 != 1: result.next = ListNode(head.val) result = result.next result.next = ListNode(tmp_val) result = result.next tmp_val = "None" else: tmp_val = head.val head = head.next if tmp_val != "None": result.next = ListNode(tmp_val) result = result.next return r.next
