【剑指Offer】链表中倒数第k个字节

给定一个链表: 1->2->3->4->5, 和 k = 2.

返回链表 4->5.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode getKthFromEnd(ListNode head, int k) {
        // 初始化former，latter
        ListNode former = head,latter = head;
        // former 先向前走 k 步
        for (int i = 0;i < k;i ++) {
            former = former.next;
        }
        // 当 former 不为空的时候，former和latter共同向前走一步
        while (former != null) {
            former = former.next;
            latter = latter.next;
        }
        return latter;
    }
}