203. 移除链表元素
删除链表中等于给定值 val 的所有节点。
示例:
输入: 1->2->6->3->4->5->6, val = 6
输出: 1->2->3->4->5
解法1
class Solution:
def removeElements(self, head, val):
if head:
while head.val == val: #遇到需要删除的元素
head = head.next #直接指向下一个元素
if head is None: #链表尾节点直接return
return head
q = head #当前
p = q.next #后继
while p: #后继不为空
if p.val == val: #后继需要删除
q.next = p.next #当前的next指向后继的next
else:
q = q.next
p = p.next
return head
解法2
class Solution:
def removeElements(self, head, val):
L = pre = ListNode(0)
pre.next = head
p = head
while p :
if p.val == val:
pre.next = p.next
del(p)
p = pre.next
else:
pre = pre.next
p = p.next
return L.next
解法3
class Solution:
def removeElements(self, head, val):
dummy_head = ListNode(-1)
dummy_head.next = head
prev = dummy_head
while prev.next is not None:
if prev.next.val == val:
prev.next = prev.next.next
else:
prev = prev.next
return dummy_head.next
解法4
递归求解:
class Solution:
def removeElements(self, head, val):
if head is None:
return None
head.next = self.removeElements(head.next, val)
return head.next if head.val == val else head
