【python3】leetcode 19. Remove Nth Node From End of List （Medium）

本文链接：https://blog.youkuaiyun.com/maotianyi941005/article/details/86250243

本文探讨了在给定链表中删除倒数第N个节点的有效算法，提供了三种实现方法：使用额外空间存储节点、不使用额外空间的一次遍历以及通过添加虚拟节点简化边界情况。每种方法都附有详细的代码实现。

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19. Remove Nth Node From End of List （Medium）

Given a linked list, remove the n-th node from the end of list and return its head.

Example:
Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5.
Note:

Given n will always be valid.

Follow up:

Could you do this in one pass?

1 万能遍历存list打遍天下:D

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

class Solution:
    def removeNthFromEnd(self, head, n):
        """
        :type head: ListNode
        :type n: int
        :rtype: ListNode
        """
        node = head
        A = []
        while(node):
            A.append(node)
            node = node.next
        if n == 1:
            if len(A) >=2:A[-2].next = None
            else:return []
        elif n == len(A):
            A[0] = A[1]
        else:
            A[len(A) - n -1 ].next = A[len(A)-n+1]
        return A[0]

2 no extra n space

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

class Solution:
    def removeNthFromEnd(self, head, n):
        """
        :type head: ListNode
        :type n: int
        :rtype: ListNode
        """
        node = head

        length = 0
        while(node):
            length += 1
            node = node.next
        if length == 1 and n==1:return []
        if length == n:return head.next
        node = head
        pre = head
        
        for i in range(length - n - 1):
            length -= 1
            pre = pre.next
        pre.next = pre.next.next
        return node

3 添加虚拟节点来避免corner case

class Solution:
    def removeNthFromEnd(self, head, n):
        """
        :type head: ListNode
        :type n: int
        :rtype: ListNode
        """
        node = head
        length = 0
        while(node):
            length += 1
            node = node.next

        dummy = ListNode(0)
        dummy.next = head
        node = dummy
        for i in range(length - n):
            node = node.next
        node.next = node.next.next
        return dummy.next