python刷题-单链表_dummy = listnode(0, head)

题目：

给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。

力扣

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next
 
# 个人题解：双指针
class Solution:
    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
        # 这里可以构造一个前驱节点指向头结点，会少一些判断情况，具体看官方题解
        node = head
        pre = node
        arrow = node.next
        for i in range(n-1):
            arrow = arrow.next
        while arrow:
            pre = node
            node = node.next
            arrow = arrow.next
        if head == node:
            return head.next
        else:
            pre.next = node.next
            del node
            return head
 
# 暴力
class Solution:
    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
        def getLength(head: ListNode) -> int:
            length = 0
            while head:
                length += 1
                head = head.next
            return length
        dummy = ListNode(0, head)
        length = getLength(head)  # 获取链表长度
        cur = dummy
        for i in range(1, length - n + 1):
            cur = cur.next
        cur.next = cur.next.next
        return dummy.next
 
# 栈实现
class Solution:
    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
        dummy = ListNode(0, head)
        stack = list()
        cur = dummy
        while cur:
            stack.append(cur)
            cur = cur.next
 
        for i in range(n):
            stack.pop()
 
        prev = stack[-1]
        prev.next = prev.next.next
        return dummy.next