剑指offer-问题15

package offer;

/**
 * offer interview 15
 */
public class Test15 {

    public static class ListNode{
        int value;
        ListNode next;

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

    public static ListNode findKthToTail(ListNode head,int k){
        if (k < 1 || head == null){
            return null;
        }

        ListNode pointer = head;

        for (int i = 1 ; i < k;i ++){
            if (pointer.next != null){
                pointer = pointer.next;
            }else{
                return null;
            }
        }

        while (pointer.next != null){
            head = head.next;
            pointer = pointer.next;
        }

        return head;
    }

    public static void main(String[] args){
        ListNode head = new ListNode(1);
        head.next = new ListNode(2);
        head.next.next = new ListNode(3);
        head.next.next.next = new ListNode(4);
        head.next.next.next.next = new ListNode(5);
        head.next.next.next.next.next = new ListNode(6);
        head.next.next.next.next.next.next = new ListNode(7);
        head.next.next.next.next.next.next.next = new ListNode(8);
        head.next.next.next.next.next.next.next.next = new ListNode(9);

        System.out.println(findKthToTail(head,1).value);
        System.out.println(findKthToTail(head,5).value);
        System.out.println(findKthToTail(head,9).value);

        System.out.println(findKthToTail(head,10).value);



    }

}