動機

複習Linked list的remove

Problem

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 = 6Output: [1,2,3,4,5]

Example 2:

Input: head = [], val = 1Output: []

Example 3:

Input: head = [7,7,7,7], val = 7Output: []

 

Constraints:

  • The number of nodes in the list is in the range [0, 104].
  • 1 <= Node.val <= 50
  • 0 <= val <= 50

Sol

class Solution:
    def removeElements(self, head: ListNode, val: int) -> ListNode:
        if head:
            prev, ret = None, head
            while ret and ret.val == val:
                ret = ret.next
            cur = ret
            while cur:
                if cur.val == val:
                    prev.next = cur.next
                else:
                    prev = cur
                cur = cur.next
            return ret
        else:
            return head