删除链表中的元素

/**
 * https://leetcode-cn.com/problems/remove-linked-list-elements/
 * 删除链表中等于给定值 val 的所有节点。
 *
 * 输入: 1->2->6->3->4->5->6, val = 6
 * 输出: 1->2->3->4->5
 */
public class RemoveListElements203 {

    public class ListNode {
        int val;
        ListNode next;
        ListNode(int x) { val = x; }
    }

/**
 * 带虚拟头节点的链表
 * @param head
 * @param val
 * @return
 */
public ListNode removeElements(ListNode head, int val) {
    if(head == null) return head;
    ListNode dummyHead = new ListNode( -1);
    dummyHead.next = head;
    ListNode pre = dummyHead;
    while(pre.next != null){
        if(pre.next.val == val){
            ListNode tempNode = pre.next;
            pre.next = tempNode.next;
        }else
            pre = pre.next; //为了防止紧接着下一个也是要删除的对象
    }
    return dummyHead.next;
}

/**
 * 不带虚拟头节点的链表
 * @param head
 * @param val
 * @return
 */
public ListNode removeElements2(ListNode head, int val) {
    while (head != null && head.val == val){
        head = head.next;
    }

    if(head == null)
        return null;

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

}