链表中倒数第k个节点（剑指offer-14）

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

     ListNode(int val) {
         this.val = val;
     }
 }*/
 public class Solution {
     public ListNode FindKthToTail(ListNode head,int k) {
         ListNode P2 = head;//head其实就是P1节点，让P2和P1指向链表开头
         while(k != 0){
             if(P2 == null){//k超出链表长度，直接返回null
                 return null;
             }
             P2 = P2.next;
             k--;
         }
         while(P2 != null){//同时移动P1和P2
             P2 = P2.next;
             head = head.next;
         }
         return head;
     }
 }