给你单链表的头节点 head
,请你反转链表,并返回反转后的链表。
示例 1:
输入:head = [1,2,3,4,5]
输出:[5,4,3,2,1]
双指针:
class Solution {
public ListNode reverseList(ListNode head) {
ListNode dummy = new ListNode(0,head);
ListNode pre = null;
ListNode cur = dummy.next;
while(cur != null){
ListNode temp = cur.next;
cur.next = pre;
pre = cur;
cur = temp;
}
return pre;
}
}
递归:
class Solution {
public ListNode reverseList(ListNode head) {
return reverse(null,head);
}
private ListNode reverse(ListNode pre,ListNode cur){
if(cur == null){
return pre;
}
ListNode temp = cur.next;
cur.next = pre;
return reverse(cur,temp);
}
}