rearrangeLastN - Java

Question

I am struggling to understand given the below solution how the first half of the linked list is joined to the back end. I've ran through it logically but cannot understand the referencing of the last 3 lines.

Given a singly linked list of integers l and a non-negative integer n, move the last n list nodes to the beginning of the linked list.

For example, for the inputs l = [1, 2, 3, 4, 5] and n = 3, the output of rearrangeLastN(l, n) should be [3, 4, 5, 1, 2].

// Singly-linked lists are already defined with this interface:
// class ListNode<T> {
//   ListNode(T x) {
//     value = x;
//   }
//   T value;
//   ListNode<T> next;
// }
//

ListNode<Integer> rearrangeLastN(ListNode<Integer> l, int n) {

    if (l == null || n == 0) return l;

    ListNode<Integer> fast = l; //1,2,3,4,5
    ListNode<Integer> slow = l; //1,2,3,4,5

    while(n > 0 && fast != null) { //3->2->1

        fast = fast.next; //4->5
        n--; //1
    }

    if (n >= 0 && fast == null) return l;

    while (fast.next != null) {  //1 Interation (4->5->null)
    
        slow = slow.next; //2->3->4->5
    
        fast = fast.next; //5
    }

    ListNode newHead = slow.next; //3->4->5

    slow.next = null; 

    fast.next = l; 

    return newHead;
}

Answer 1

Initially:

1 -> 2 -> 3 -> 4 -> 5 -> null
^
l
fast
slow

After the 1st while loop:

1 -> 2 -> 3 -> 4 -> 5 -> null
^              ^
l         
               fast
slow

After the 2nd while loop:

1 -> 2 -> 3 -> 4 -> 5 -> null
^    ^              ^
l         
                    fast
     slow

After the line ListNode newHead = slow.next;:

1 -> 2 -> 3 -> 4 -> 5 -> null
^    ^    ^         ^
l         
                    fast
     slow newHead

After the line slow.next = null;:

1 -> 2 -> null    3 -> 4 -> 5 -> null
^    ^            ^         ^
l         
                            fast
     slow         newHead

After the line fast.next = l;:

┌────────────────────────────────┐
└> 1 -> 2 -> null    3 -> 4 -> 5 ┘
   ^    ^            ^         ^
   l         
                               fast
        slow         newHead