[LeetCode] Remove LinkedList Elements

Problem

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

Note

链表基本的删除操作，最好掌握以下三种方法。

Solution

Dummy Node

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

Recursion

public class Solution {
    public ListNode removeElements(ListNode head, int val) {
        if (head == null) return head;
        head.next = removeElements(head.next, val);
        return head.val == val ? head.next : head;
    }
}

Iteration

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;
    }
}