CC2.2.java

public int kthToLast(ListNode head, int k) {
        if(head == null)
            return -1;
        ListNode p1, p2;
        p1 = p2 = head;
        for(int i = 0; p1 != null && i < k; i++) {
            p1 = p1.next;
        }
        while(p1 != null) {
            p1 = p1.next;
            p2 = p2.next;
        }
        return p2.val;
    }