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.)
Example 1:
Input: head = [1,2,3,4]
Output: [2,1,4,3]
Explanation:
Example 2:
Input: head = []
Output: []
Example 3:
Input: head = [1]
Output: [1]
Example 4:
Input: head = [1,2,3]
Output: [2,1,3]
Constraints:
- The number of nodes in the list is in the range
[0, 100]. 0 <= Node.val <= 100
Solution
Python3
# 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]:
res = curr = ListNode(-1, head)
while curr.next and curr.next.next:
first, second = curr.next, curr.next.next
following = curr.next.next.next
first.next, second.next, curr.next = following, first, second
curr = first
return res.next