「这是我参与11月更文挑战的第6天，活动详情查看：2021最后一次更文挑战」
描述
Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head.
Example 1:
Input: head = [1,2,6,3,4,5,6], val = 6
Output: [1,2,3,4,5]
Example 2:
Input: head = [], val = 1
Output: []
Example 3:
Input: head = [7,7,7,7], val = 7
Output: []
Note:
The number of nodes in the list is in the range [0, 10^4].
1 <= Node.val <= 50
0 <= val <= 50
解析
根据题意，就是给出了一个链表的头节点 head 和一个整数 val ，题目要求我们移除链表中所有值和 val 相等的节点，并返回处理之后的新的链表的头。这个题就是考察我们对删除链表节点的基本操作，直接新建一个链表头节点 result ，然后遍历链表中的每个节点，如果节点的值和 val 不一样，就新建一个和当前节点一样值的节点连接到 result 后面，遍历结束，最后返回 result.next 即可。
解答
class ListNode(object):
def __init__(self, val=0, next=None):
self.val = val
self.next = next
class Solution(object):
def removeElements(self, head, val):
"""
:type head: ListNode
:type val: int
:rtype: ListNode
"""
if not head:return head
result = ListNode(0, None)
tmp = result
while head:
if head.val!=val:
tmp.next = ListNode(head.val, None)
tmp = tmp.next
head = head.next
return result.next
运行结果
Runtime: 76 ms, faster than 35.99% of Python online submissions for Remove Linked List Elements.
Memory Usage: 23.7 MB, less than 6.39% of Python online submissions for Remove Linked List Elements.
解析
可以在原链表上直接进行操作，这样直接快速遍历一次即可完成，并且能节省新的内存开销。思路也很简单：
- 先 while 循环找到头节点 head 不为 val 的位置
- 然后将 head 赋值给 result ，让 result 保存头节点
- 当 head 不为空的时候一直执行 while 循环，如果当前节点的下个节点不为空且值为 val ，则将 head.next = head.next.next ，否则则直接 head = head.next 进行之后的节点遍历。
- 循环结束 返回 result
解答
class ListNode(object):
def __init__(self, val=0, next=None):
self.val = val
self.next = next
class Solution(object):
def removeElements(self, head, val):
"""
:type head: ListNode
:type val: int
:rtype: ListNode
"""
if not head:return head
while head and head.val==val:
head = head.next
result = head
while head :
if head.next and head.next.val == val:
head.next = head.next.next
else:
head = head.next
return result
运行结果
Runtime: 56 ms, faster than 94.53% of Python online submissions for Remove Linked List Elements.
Memory Usage: 20.4 MB, less than 13.14% of Python online submissions for Remove Linked List Elements.
原题链接：leetcode.com/problems/re…
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