19. Remove Nth Node From End of List - LeetCode

from typing import Optional


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


class Solution1:
    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
        l = r = d = ListNode(next=head)
        for _ in range(n - 1):
            r = r.next
        while r.next and r.next.next is not None:
            l, r = l.next, r.next
        l.next = l.next.next
        return d.next


class Solution:
    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
        l = r = head
        for _ in range(n):
            r = r.next
        if r is None:
            return head.next
        while r.next:
            l, r = l.next, r.next
        l.next = l.next.next
        return head