206. Reverse Linked List

Reverse a singly linked list.

Example:

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

SOLUTION

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

Runtime: 0 ms, faster than 100.00% of Java online submissions for Reverse Linked List.
Memory Usage: 37.7 MB, less than 100.00% of Java online submissions for Reverse Linked List.