reverse_list.java

public class Node {
  int val;
  Node next;
}

public Node reverseList(Node head) {
  if (head == null || head.next == null) {
    return head;
  }
  
  Node newHead = new Node();
  while(head.next != null) {
    Node cur = head.next;
    head.next = cur.next;
    cur.next = newHead.next;
    newHead.next = cur;
  }
}