定义一个函数,输入一个链表的头节点,反转该链表并输出反转后链表的头节点。
示例:
输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL
限制:
0 <= 节点个数 <= 5000
题解:
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode reverseList(ListNode head) {
//迭代
ListNode pre = null, cur = head, next = null;
while(cur != null) {
next = cur.next;
cur.next = pre;
pre = cur;
cur = next;
}
return pre;
//递归
// if(head == null || head.next == null) return head;
// ListNode node = reverseList(head.next);
// head.next.next = head;
// head.next = null;
// return node;
}
}