206. Reverse Linked List

Reverse a singly 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) {
        
       ArrayList<Integer> vals = new ArrayList<Integer>();
       
       ListNode check = head;
       
       while (check != null){
           vals.add(check.val);
           check = check.next;
       }
       
       ListNode checkNew = head;
       int i = 0;
       
       for (i = vals.size()-1 ; i >= 0; i--){
           
           checkNew.val = vals.get(i);
           checkNew = checkNew.next;
           
       }
       
       return head; // can change head to check, same thing
        
    }
}