203. Remove Linked List Elements

Remove Linked List Elements

Remove all elements from a linked list of integers that have value val.

Example Given: 1 --> 2 --> 6 --> 3 --> 4 --> 5 --> 6, val = 6 Return: 1 --> 2 --> 3 --> 4 --> 5

Credits:Special thanks to @mithmatt for adding this problem and creating all test cases.

Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode removeElements(ListNode head, int val) {
        if (head == null) return null;

        // find head
        ListNode result = head;
        while (result != null && result.val == val) {
            result = result.next;
        }


        if (result == null) {
            return null;
        }

        ListNode runner = result;
        while (runner.next != null) {
            if (runner.next.val == val) {
                runner.next = runner.next.next;
            } else {
                runner = runner.next;
            }
        }

        return result;
    }
}