Remove Nth Node From End of List

lcpy gen -n 19   # by problem number
lcpy gen -s remove_nth_node_from_end_of_list   # by problem name

Input: head = [1,2,3,4,5], n = 2
Output: [1,2,3,5]

Input: head = [1], n = 1
Output: []

Input: head = [1,2], n = 1
Output: [1]

from leetcode_py import ListNode


class Solution:
    # Time: O(L) where L is the length of the list
    # Space: O(1)
    def remove_nth_from_end(self, head: ListNode[int] | None, n: int) -> ListNode[int] | None:
        dummy = ListNode(0)
        dummy.next = head
        fast: ListNode[int] | None = dummy
        slow: ListNode[int] | None = dummy

        # Move fast pointer n+1 steps ahead
        for _ in range(n + 1):
            assert fast
            fast = fast.next

        # Move both pointers until fast reaches end
        while fast:
            fast = fast.next
            assert slow
            slow = slow.next

        # Remove the nth node
        assert slow and slow.next
        slow.next = slow.next.next
        return dummy.next