19删除排序链表中的重复元素

给定一个排序链表，删除所有重复的元素，使得每个元素只出现一次。

示例 1:
输入: 1->1->2
输出: 1->2

示例 2:
输入: 1->1->2->3->3
输出: 1->2->3

class Solution:
    def deleteDuplicates(self, head: ListNode) -> ListNode:
        node=head
        while node and node.next:
            if node.val==node.next.val:
                node.next=node.next.next
            else:
                node=node.next
        return head

class Solution:
    def deleteDuplicates(self, head: ListNode) -> ListNode:
        dummy_head = ListNode(None)
        dummy_head.next = head

        pre = dummy_head
        cur = head

        while cur:
            if pre and cur.val == pre.val:
                pre.next = cur.next
                cur.next = None
                cur = pre.next
                continue

            pre = cur
            cur = cur.next
        return dummy_head.next

class Solution:
    def deleteDuplicates(self, head: ListNode) -> ListNode:
        if head is None or head.next is None:
            return head
        
        child = self.deleteDuplicates(head.next)
        if child and head.val == child.val:
            head.next = child.next
            child.next = None
            
        return head

来源：力扣（LeetCode）