Leetcode # 203. Remove Linked List Elements

https://leetcode.com/problems/remove-linked-list-elements/

Solution 1

class Solution:
  def removeElements(self, head: Optional[ListNode], val: int) -> Optional[ListNode]:
    new_head = head
    while new_head is not None and new_head.val == val:
      new_head = new_head.next

    cur = new_head
    while cur:
      while cur.next is not None and cur.next.val == val:
        cur.next = cur.next.next
      cur = cur.next

    return new_head

注意事項

1. new_head其值是否為val
2. 當跳過某一個值為val的node時，下一個node是否其值也為val

Solution 2

Time Complexity: O(len(linked_list))
Space Complexity: O(1)
(The input and output generally do not count towards the space complexity.)

注意：
root = ListNode(0, head)
pre, cur = root, head
 root, pre, cur = ListNode(0, head), root, head
由於多重賦值是先計算右側，所以會有 root 尚未宣告的 error

class Solution:
  def removeElements(self, head: Optional[ListNode], val: int) -> Optional[ListNode]:
    root = ListNode(0, head)
    pre, cur = root, head
    while cur:
      if cur.val == val:
        while cur and cur.val == val:
            cur = cur.next
        pre.next = cur
      else:
        pre, cur = cur, cur.next
    return root.next

Last Updated on 2024/06/08 by A1go