Middle of the Linked List

/**
 * 876. Middle of the Linked List
 * <p>
 * Given a non-empty, singly linked list with head node head, return a middle node of linked list.
 * <p>
 * If there are two middle nodes, return the second middle node.
 * <p>
 * Example 1:
 * <p>
 * Input: [1,2,3,4,5]
 * Output: Node 3 from this list (Serialization: [3,4,5])
 * The returned node has value 3.  (The judge's serialization of this node is [3,4,5]).
 * Note that we returned a ListNode object ans, such that:
 * ans.val = 3, ans.next.val = 4, ans.next.next.val = 5, and ans.next.next.next = NULL.
 * Example 2:
 * <p>
 * Input: [1,2,3,4,5,6]
 * Output: Node 4 from this list (Serialization: [4,5,6])
 * Since the list has two middle nodes with values 3 and 4, we return the second one.
 */
public class MiddleNodeOfLinkedList {
	public ListNode middleNode(ListNode head) {

		ListNode slowPtr = head;
		ListNode fastPtr = head;

		while (fastPtr != null && fastPtr.next != null) {
			slowPtr = slowPtr.next;
			fastPtr = fastPtr.next.next;
		}

		return slowPtr;
	}
}