12.1 Reverse Linked List (Easy)

Reverse a singly linked list.

A linked list can be reversed either iteratively or recursively. Could you implement both?

https://leetcode.com/problems/reverse-linked-list/

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

        ListNode next=null;
        ListNode previous=null;
        ListNode current=head;

        while(current!=null){
            next=current.next;
            current.next=previous;
            previous=current;
            current=next;
        }
        return previous;
    }
}