Reverse Linked List

Reverse a singly linked list.

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

Solution

/**
 * 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 null;
        if (head.next == null) return head;

        ListNode next = head.next;

        ListNode result = reverseList(next);
        head.next = null;
        next.next = head;

        return result;
    }
}