leetcode203.移除链表元素

题比较简单，注意一些细节，比如pre的重定位

/**
 * 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) {
           
           //定义“指针”
           ListNode dummyhead = new ListNode(-1,head);
           ListNode pre = dummyhead;
           ListNode cur = head;
 
           while(cur != null) {
                //两种情况pre都要走
                if( val == cur.val) {
                    pre.next = cur.next;
                } else {
                    pre = cur;
                }
                cur = cur.next;
           }
 
           return dummyhead.next;
 
 
    }
}