移除整数链表中所有与 val 值相同的元素。

举例：
输入： 1->2->6->3->4->5->6, val = 6
输出： 1->2->3->4->5

/*
 * 203. Remove Linked List Elements
 * https://leetcode.com/problems/remove-linked-list-elements/
 * https://www.whosneo.com/203-remove-linked-list-elements/
 */

public class RemoveElements {
    public static void main(String[] args) {
        ListNode head = new ListNode(1);
        ListNode node = head;
        for (int i = 2; i < 10; i++) {
            node.next = new ListNode(i);
            node = node.next;
        }
        node.next = new ListNode(6);
        node = node.next;
        node.next = new ListNode(3);

        RemoveElements solution = new RemoveElements();

        solution.print(head);
        head = solution.removeElements(head, 6);
        solution.print(head);
        head = solution.removeElements(head, 3);
        solution.print(head);
    }

    private void print(ListNode node) {
        for (; node != null; node = node.next) {
            System.out.print(node.val);
            System.out.print("->");
        }
        System.out.println("null");
    }

    private ListNode removeElements(ListNode head, int val) {
        while (head != null && head.val == val)
            head = head.next;
        if (head == null)
            return null;
        ListNode node = head;
        while (node.next != null) {
            if (node.next.val == val)
                node.next = node.next.next;
            else
                node = node.next;
        }
        return head;
    }
}