思想：删除倒数第n个节点相当于删除正数第len-n+1个节点，要删去它，找其前驱
class Solution { public ListNode removeNthFromEnd(ListNode head, int n) { if(head==null)return head; int len = 0; ListNode temp = head; while(temp!=null){ len++; temp = temp.next; } int k = len-n;//倒数第n个节点相当于正数第len-n+1个节点，要删去它，找其前驱 temp = head; if(k==0){ return head.next; } while((--k)>0){ temp = temp.next; } temp.next = temp.next.next; return head; } }