双指针-链表

/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode FindKthToTail(ListNode head,int k) {
        if (head == null || k <= 0) {
            return null;
        }
        int length = 1 ;
        ListNode temp = head;
        while(true){
            if(temp.next == null){
                break;
            }
            length++;
            temp = temp.next;
        }
        if(k > length){
            return null;
        }
        int pos_k = length - k;
        ListNode temp1 = head;
        int pos_num = 0;
        while(pos_num < pos_k){
            temp1 = temp1.next;
            pos_num++;
        }
        return temp1;
    }
}

这道题是考链表的熟悉度，还是双指针的问题

抄的高赞的

    public ListNode FindKthToTail(ListNode head,int k) {
        if(head == null || k ==0 ){
            return null;
        }

        ListNode slow=head;
        ListNode fast=head;
        for(int i=0; i < k;i++){
            if(fast == null){
                return null;
            }
            fast = fast.next;
        }
        while(fast!=null){
            slow=slow.next;
            fast=fast.next;
        }
        return slow;
    }