From LeetCode 24. Swap Nodes in Pairs
Description
Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list’s nodes (i.e., only nodes themselves may be changed.)
Input: head = [1,2,3,4]
Output: [2,1,4,3]
Solution
class Solution:
def swapPairs(self, head: ListNode) -> ListNode:
res = ListNode(next=head)
pre = res
# we have to make sure pre.next and pre.next.next are not null value, otherwise swap has ended
while pre.next and pre.next.next:
cur = pre.next
post = pre.next.next
# pre，cur，post corresponds to leftmost, middle and rightmost nodes
cur.next = post.next
post.next = cur
pre.next = post
pre = pre.next.next
return res.next
Credit to yuzhoujr