Reverse Linked List

Description

Reverse a singly linked list.

Example:

Input: 1->2->3->4->5->NULL

Output: 5->4->3->2->1->NULL

Follow up:

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

Code

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