876. Middle of the Linked List java

https://leetcode.com/problems/middle-of-the-linked-list/?envType=study-plan&id=level-1

class Solution {
    public ListNode middleNode(ListNode head) {
        Map<Integer, ListNode> map = new HashMap();
        
        int i = 0;
        for (; head != null; i++) {
            map.put(i, head);
            head = head.next;
        }

        int middle = Math.round(i/2);

        return map.get(middle);
    }
}