LC 0024 [M] Swap Nodes in Pairs - ALawliet/algorithms GitHub Wiki
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution:
def swapPairs(self, head: Optional[ListNode]) -> Optional[ListNode]:
dummy = ListNode(0, head)
prev, cur = dummy, head
while cur and cur.next:
# save ptrs
nxtPair = cur.next.next
second = cur.next
# reverse this pair
second.next = cur
cur.next = nxtPair
prev.next = second
# update ptrs
prev = cur
cur = nxtPair
return dummy.next