代码随想录算法训练营第三天| 链表

203 移除链表元素

class Solution {
    public ListNode removeElements(ListNode head, int val) {
        if (head == null) {
            return head;
        }
        // 因为删除可能涉及到头节点，所以设置dummy节点，统一操作
        ListNode dummy = new ListNode(-1, head);
        ListNode pre = dummy;
        ListNode cur = head;
        while (cur != null) {
            if (cur.val == val) {
                pre.next = cur.next;
            } else {
                pre = cur;
            }
            cur = cur.next;
        }
        return dummy.next;
    }
}

206. 反转链表

class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode pre = null;
        ListNode cur = head;
        while (cur != null) {
            ListNode temp = cur.next;
            cur.next = pre;

            pre = cur;
            cur = temp;
        }

        return pre;
    }
}