List

203. Remove Linked List Elements

Recursive

class Solution:
    def removeElements(self, head: ListNode, val: int) -> ListNode:
        if head is None:return None
        head.next = self.removeElements(head.next, val)
        return head.next if head.val==val else head

Iterative

class Solution:
    def removeElements(self, head: ListNode, val: int) -> ListNode:
        dummy = ListNode(-1)
        dummy.next = head
        node = head
        prev = dummy
        while node is not None:
            if node.val==val:
                prev.next = node.next
                node.next = None
                node = prev.next
            else:
                prev = node
                node = node.next
        return dummy.next