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203. remove linked list elements

admin 11月 13, 2020 0

Remove all elements from a linked list of integers that have value val.

Example:
1
2
3
> Input:  1->2->6->3->4->5->6, val = 6
> Output: 1->2->3->4->5
>

思路

pre —> 通过检验的Node

dummy —> 标记head pre, 防止head消失

Note：val相等的情况有可能连续出现，所以只有已验证 != val, 才能pre = pre.next

Note2: 如果写while pre.next, 前面要有while pre

所以: while pre and pre.next


# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class :
    def removeElements(self, head, val):
        """
        :type head: ListNode
        :type val: int
        :rtype: ListNode
        """
        pre = dummy = ListNode(-1)
        dummy.next = head
        
        while pre and pre.next:
            if pre.next.val == val:
                pre.next = pre.next.next
            else:
                pre = pre.next
        
        return dummy.next