0024: Swap Nodes in Pairs

Problem Statement

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

Code Solution

class Solution:
    def swapPairs(self, head: Optional[ListNode]) -> Optional[ListNode]:
        
        head = temp = ListNode(-1, head)
        while temp and temp.next and temp.next.next:
            node_plus_1 = temp.next
            node_plus_2 = temp.next.next
            node_plus_3 = temp.next.next.next
            
            node_plus_1.next = node_plus_3
            node_plus_2.next = node_plus_1
            temp.next = node_plus_2
            
            temp = temp.next.next
	        
        return head.next