RemoveNthNodeFromEndofList.py

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
        current, nth = head, ListNode(val=None, next=head)        
        while current:
            current = current.next
            if n > 0:
                n -= 1
            else:
                # only advance nth after the sub list has nth elements
                nth = nth.next        
        if nth.val is None:
            # head is the next element
            return head.next
        else:
            nth.next = nth.next.next if nth.next else None
            return head