*Remove Linked List Elements

题目：

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

解法一：

/**
 * 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;
        ListNode dummy=new ListNode(0);
        dummy.next=head;
        ListNode pre=dummy;
        ListNode cur=head;
        while(cur!=null){
            if(cur.val==val){
                pre.next=cur.next;
                cur=cur.next;
            }else{
                pre=cur;
                cur=cur.next;
            }
        }
        return dummy.next;
    }
}

解法二：

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

reference：

http://www.senonweb.com/?p=517

http://bookshadow.com/weblog/2015/04/24/leetcode-remove-linked-list-elements/