LeetCode 19. 删除链表的倒数第N个节点

示例：
给定一个链表: 1->2->3->4->5, 和 n = 2.
当删除了倒数第二个节点后，链表变为 1->2->3->5.
说明：
给定的 n 保证是有效的。

# 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:
        if head.next == None: return None
        deleteIndex = n
        deleteNode: ListNode = head
        rightNode = head
        #right先走一段
        while deleteIndex > 0:
            deleteIndex -= 1
            rightNode = rightNode.next
        if rightNode == None:#删除第一个节点
            head = head.next
            return head;
        while rightNode.next != None:
            rightNode = rightNode.next
            deleteNode = deleteNode.next
        if n == 1:#删除最后一个节点
            deleteNode.next = None
        else:
            deleteNode.next = deleteNode.next.next
        return head