Leetcode 203 : Remove Linked List Elements

Solution to Remove Linked List Elements Problem. The first approach uses a dummy pointer to handle the edge case of removing head node itself.

Approach 1:

public class Solution {
    public ListNode removeElements(ListNode head, int val) {
        ListNode dummy = new ListNode();
        dummy.val = -1;
        dummy.next = head;
        
        ListNode cur = head;
        ListNode pre = dummy;
        while(cur != null) {
            if(cur.val == val) {
                pre.next = cur.next;
            } else {
                pre = cur;
            }    
            cur = cur.next;
        }
        
        return dummy.next;
    }
}

Approach 2:

Approach 2 is more cleaner with less variables. Here is a video explaining the same.

public class Solution {
    public ListNode removeElements(ListNode head, int val) {
        while(head != null && head.val == val) {
            head = head.next;
        }
        
        ListNode cur = head;
        while(cur != null && cur.next != null) {
            if(cur.next.val == val) {
                cur.next = cur.next.next;
            } else {
                cur = cur.next;
            }
        }
        return head;
    } 
}