203. Remove Linked List Elements

Problem

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.

  Example 1:

Input: head = [1,2,6,3,4,5,6], val = 6
Output: [1,2,3,4,5]

Example 2:

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

Example 3:

Input: head = [7,7,7,7], val = 7
Output: []

  Constraints:

• The number of nodes in the list is in the range [0, 10^4].

• 1 <= Node.val <= 50

• 0 <= val <= 50

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) {
        if (head == null) {
            return null;
        }
        while (head != null && head.val == val) {
            head = head.next;
        }
        ListNode r = head;
        ListNode t = head;
        while (r != null) {
            if (r.val == val) {
                t.next = r.next;
            } else {
                t = r;
            }
            r = r.next;
        }
        return head;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).