[leetcode-24] Swap-Nodes-In-Pairs_2

LeetCode-24

swap-nodes-in-pairs_2 : 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

note : only nodes themselves may be changed.

MyAnswer

        :::python

# 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]:
        root = prev = ListNode(None)
        prev.next = head
        while head and head.next:
            b = head.next
            head.next = b.next
            b.next = head
            prev.next = b
            head = head.next
            prev = prev.next.next
        return root.next

Result : 32ms Memory: 13.9mb