0203 - Remove Linked List Elements

0203 - Remove Linked List Elements

Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head.

Examples

Input: head = [1,2] Output: [2,1]

Input: head = [] Output: []

Constraints:

The number of nodes in the list is the range [0, 5000]. -5000 <= Node.val <= 5000

Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?

Java Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeElements(ListNode head, int val) {
        ListNode result = new ListNode(0);
        result.next = head;
        
        ListNode previous = result;
        ListNode current = head;
        
        while(current != null) {
            if(current.val == val) {
                previous.next = current.next;
            } else {
                previous = current;
            }
            current = current.next;
        }
        return result.next;
    }
}