Given the head of a singly linked list, reverse the list, and return the reversed list.
Example 1:
Input: head = [1,2,3,4,5]
Output: [5,4,3,2,1]
Example 2:
Input: head = [1,2]
Output: [2,1]
Example 3:
Input: head = []
Output: []
Constraints:
- The number of nodes in the list is the range [0, 5000].
- -5000 <= Node.val <= 5000
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
class Solution {
public ListNode reverseList(ListNode head){
if(head==null||head.next==null){
return head;
}
ListNode pre = null;
ListNode now = head;
while(now!=null){
ListNode next = now.next;
now.next = pre;
pre = now;
now = next;
}
return pre;
}
}