CC150 : Kth to last Element of Linked List

递归版，因为既要传一个node也要传数字回来，所以只能写个wrapper。

class Solution {
    class IntWrapper {
	public int value = 0;
    }
	
    public ListNode kthLast(ListNode head， int k， IntWrapper i) {
	if(head == null) return null;
	ListNode node = kthLast(head.next, k, i);
	i.value = i.value + 1;
	if(k == i.value) {
	    node = head;
	}
	return node;
    }
}

非递归版： 

class Solution {
    public ListNode kthLast(ListNode head, int k) {
        ListNode l1 = head, l2 = head;
        for(int i = 0; i < k; i++) {
            if(l2 == null) return null;
            l2 = l2.next;
        }
        while(l2 != null) {
            l1 = l1.next;
            l2 = l2.next;
        }
        return l1;
    }
}