2.2 Implement an algorithm to find the kth to last element of a singly linked list.

2.2 linkedListKthToLast

ListNode {
    int val;
    ListNode next;
    ListNode(int val) {
        this.val = val;
        next = null;
    }
}

ListNode linkedListKthToLast(ListNode head, int k) {
    if (head == null || k < 1) {
        return null;
    }
    
    ListNode slow = head;
    ListNode fast = head;
    for (int i = 2; i <= k; i++) {
        fast = fast.next;
        if (fast == null) {
            return null;
        }
    }
    
    while (fast.next != null) {
        slow = slow.next;
        fast = fast.next;
    }
    
    return slow;
}