Remove Linked List Elements

Problem

Remove every node with value equal to val from the linked list.

Constraints

• 0 ≤ length ≤ 10⁴

Approach — Linked List

This is a Linked List problem. The idea: rework the list with careful pointer manipulation — often a dummy head and fast/slow pointers — in a single pass. Work through the reference code below line by line, then re-derive it yourself in the editor — that's how the pattern sticks.

Complexity: O(n) time, O(1) space.

Solution code

Python

class Solution:
    def removeElements(self, head, val):
        dummy = ListNode(0, head)
        cur = dummy
        while cur.next:
            if cur.next.val == val:
                cur.next = cur.next.next
            else:
                cur = cur.next
        return dummy.next

Java

class Solution {
    public ListNode removeElements(ListNode head, int val) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode prev = dummy;
        while (prev.next != null) {
            if (prev.next.val == val) prev.next = prev.next.next;
            else                       prev = prev.next;
        }
        return dummy.next;
    }
}

Practice it

Reading a solution isn't the same as being able to write it under pressure. Open this problem in the in-browser editor, hide the solution, and solve it from scratch — your code runs against real test cases instantly.