python-leetcode面试题解之两两交换链表中的节点.zip

''' Given a linked list, swap every two adjacent nodes and return its head. For example, Given 1->2->3->4, you should return the list as 2->1->4->3. Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed. ''' class ListNode(object): def __init__(self, x): self.val = x self.next = None class Solution(object): def swapPairs(self, head): if head == None or head.next == None: return head cur = head head = head.next while cur and cur.next: pNext = cur.next.next cur.next.next = cur if pNext: if pNext.next: cur.next = pNext.next else: cur.next = pNext else: cur.next = None cur = pNext return head # recursion def swapPairs2(self, head): if not head or not head.next: return head first, second = head, head.next third = second.next head = second second.next = first first.next = self.swapPairs(third) return head