0019-remove_nth_node_from_end_of_list.py

## Use fast and slow pointer
## Use dummy node to get rid of off-by-one issues

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
        dummy = ListNode(None)
        dummy.next = head

        slow = dummy
        fast = dummy
        for i in range(n + 1):
            fast = fast.next

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

        slow.next = slow.next.next
        return dummy.next