Leetcode 206 反转链表 Java

Leetcode 206 反转链表

//迭代
/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode reverseList(ListNode head) {
if(head==null||head.next==null) return head;
ListNode p=reverseList(head.next);
head.next.next=head;
head.next=null;
return p;

}
}

public static ListNode reverseListIterative(ListNode head) {
ListNode prev = null; //前指针节点
ListNode curr = head; //当前指针节点
//每次循环，都将当前节点指向它前面的节点，然后当前节点和前节点后移
while (curr != null) {
ListNode nextTemp = curr.next; //临时节点，暂存当前节点的下一节点，用于后移
curr.next = prev; //将当前节点指向它前面的节点
prev = curr; //前指针后移
curr = nextTemp; //当前指针后移
}
return prev;
}