206. Reverse Linked List

/*
    reverse links
*/
class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        ListNode current = head;
        ListNode next;

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

/* 
   add nodes to new head
*/
class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode cur = head;
        ListNode prev = null;
        ListNode reversedHead = head;
        while(cur != null){
            reversedHead = new ListNode(cur.val);
            reversedHead.next = prev;
            prev = reversedHead;
            cur = cur.next;
        }
        return reversedHead;
    }
}

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */