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24. Swap Nodes In Pairs

Linked List Recursion

Problem - Swap Nodes In Pairs

Medium

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

Solutions

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# 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]:
        pointer = ListNode(0, head)
        last, current = pointer, head
        while current and current.next:
            node = current.next
            current.next = node.next
            node.next = current

            last.next = node
            last, current = current, current.next
        return pointer.next

Submission Stats:

  • Runtime: 0 ms (100.00%)
  • Memory: 17.8 MB (33.37%)