203. Remove Linked List Elements

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

思路：扫一遍linkedlist，移出对应val的node。注意要用node.next，如果是用Node来遍历的话不方便去掉node。注意head也可能是要移的node。因此用dummy node以便于检查。

/**
 * 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) {
    ListNode dummy=new ListNode(-1);
    dummy.next=head;
    ListNode copy=dummy;
    while(copy.next!=null){
        if(copy.next.val==val){
            copy.next=copy.next.next;
        }else{
            copy=copy.next;
        }
    }
    return dummy.next;
}
}