LeetCode-面试题02.02-返回倒数第k个节点

输入： 1->2->3->4->5 和 k = 2
输出： 4

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public int kthToLast(ListNode head, int k) {
        if(head==null) return 0;
        ListNode fast = head;
        ListNode low = null;
        for(int i=0;i<k-1;i++){
            fast = fast.next;
        }
        low = head;
        while(fast.next!=null){
            fast = fast.next;
            low = low.next;
        }
        return low.val;
    }
}

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