[LeetCode]206. Reverse Linked List(链表反转)

Reverse a singly linked list.

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利用循环。

public class Solution {
    public ListNode reverseList(ListNode head) {
        if(head == null ||head.next == null) return head;
        ListNode pre = head;
        head = head.next;
        pre.next = null;
        while(head != null){
            ListNode next = head.next;
            head.next = pre;
            pre = head;
            head = next;
        }
        return pre;
    }
}

 递归版

public class Solution {
    public ListNode reverseList(ListNode head) {
        if(head == null ||head.next == null) return head;
        ListNode pre = head;
        head = head.next;
        ListNode newhead = reverseList(head);
        pre.next = null;
        head.next = pre;
        return newhead;
        
    }
}