Leetcode 反转链表

Day 10 刷题

####### 力扣官方解答：用节点作为交换方式，而非其中的值，通过增加一个空null，来使得指向完全相反。
#######迭代法：

class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        ListNode curr = head;
        while (curr != null) {
            ListNode next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
}

#######递归法:看不懂

class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        // 两个节点为一组，
        ListNode newHead = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return newHead;
    }
}