Leetcode 1721. Swapping Nodes in a Linked List

class Solution:
    def swapNodes(self, head: ListNode, k: int) -> ListNode:
        length = 0
        ptr = head
        while ptr:
            length += 1
            ptr = ptr.next

        ptr = head
        count = 0
        while ptr:
            count += 1
            if count == k:
                beginning = ptr
            if count == length - k + 1
                end = ptr
            ptr = ptr.next

        beginning.val, end.val = end.val, beginning.val
        return head

class Solution:
    def swapNodes(self, head: ListNode, k: int) -> ListNode:
        ptr = head
        for _ in range(1, k):
            ptr = ptr.next

        beginning = ptr
        end = head
        while ptr.next:
            ptr = ptr.next
            end = end.next
        beginning.val, end.val = end.val, beginning.val
        return head