2.删除链表指定值的节点

// head = removeValue(head, 2);
    public static Node removeValue(Node head, int num) {
        // head来到第一个不需要删的位置
        while (head != null) {
            if (head.value != num) {
                break;
            }
            head = head.next;
        }
        //head来到第一个不需要删的位置
        Node pre = head;
        Node cur = head;
        while (cur != null) {
            if (cur.value == num) {
                pre.next = cur.next;
            } else {
                pre = cur;
            }
            cur = cur.next;
        }
        return head;
    }