leetcode-solution/Python/0203-remove-linked-list-elements.py at main · hogan-tech/leetcode-solution · GitHub

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# time complexity: O(n)
# space complexity: O(1)
from typing import Optional


class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next


class Solution:
    def removeElements(self, head: Optional[ListNode], val: int) -> Optional[ListNode]:
        dummy = ListNode(0, head)
        prev = dummy
        curr = head
        while curr:
            if curr.val == val:
                prev.next = curr.next
                curr = curr.next
            else:
                prev = curr
                curr = curr.next
        return dummy.next


head = ListNode()
val = 7
print(Solution().removeElements(head, val))

head = ListNode(1)
head.next = ListNode(2)
head.next.next = ListNode(6)
head.next.next.next = ListNode(3)
head.next.next.next.next = ListNode(4)
head.next.next.next.next.next = ListNode(5)
head.next.next.next.next.next.next = ListNode(6)
val = 6
print(Solution().removeElements(head, val))

head = ListNode(7)
head.next = ListNode(7)
head.next.next = ListNode(7)
head.next.next.next = ListNode(7)
val = 7
print(Solution().removeElements(head, val))