0019-remove-nth-node-from-end-of-list.py

class Solution:
    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
        dummy = ListNode(0, head)
        left = dummy
        right = head

        while n > 0:
            right = right.next
            n -= 1

        while right:
            left = left.next
            right = right.next

        # delete
        left.next = left.next.next
        return dummy.next