easy

Reverse a singly linked list.

Hint:A linked list can be reversed either iteratively or recursively. Could you implement both?

非常好懂的視頻講解

這道題暫時(shí)只會(huì)iterative的寫法， 需要補(bǔ)充recursive的寫法

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null){
            return null;
        }
        if (head.next == null){
            return head;
        }
        ListNode prev = null;
        ListNode curt = head;
        while (curt != null){
            ListNode temp = curt.next;
            curt.next = prev;
            prev = curt;
            curt = temp;
        }
        return prev;
    }
}