LeetCode 206 Reverse Linked List

While loop 做法：

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

Recursion 做法：

class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode newHead = reverseList(head.next);
        ListNode tail = head.next;
        tail.next = head;
        head.next = null;
        return newHead;
    }
}