Remove Nth Node From End of List.py

from typing import Optional


class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next


class Solution:
    """
    Time:   O(n)
    Memory: O(1)
    """

    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
        fast = slow = head

        for k in range(n):
            fast = fast.next

        if fast is None:
            return head.next

        while fast.next:
            fast = fast.next
            slow = slow.next

        slow.next = slow.next.next

        return head