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

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

这道题创建一个新的node指向head，留作返回用。再创建一个currNode进行node操作用。首先确保currNode和currNode.next不为null，再判断currNode.next的val是不是等于target，是的话让currNode.next等于currNode.next.next，删除之前的currNode.next，不想等的话让currNode等于currNode.next，进行下面的判断。代码如下：

/**
 * 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 head;
        }
        ListNode preHead = new ListNode(0);
        preHead.next = head;
        ListNode currNode = preHead;
        while (currNode != null && currNode.next != null) {
            if (currNode.next.val == val) {
                currNode.next = currNode.next.next;
            } else {
                currNode = currNode.next;
            }
        }
        return preHead.next;
    }
}