fastrunner and slowrunner trick.(be care of head node)
1 /** 2 * Definition for singly-linked list. 3 * public class ListNode { 4 * int val; 5 * ListNode next; 6 * ListNode(int x) { 7 * val = x; 8 * next = null; 9 * } 10 * } 11 */ 12 public class Solution { 13 public ListNode removeNthFromEnd(ListNode head, int n) { 14 // IMPORTANT: Please reset any member data you declared, as 15 // the same Solution instance will be reused for each test case. 16 if(head == null) 17 return null; 18 if(n == 1) 19 { 20 ListNode runner = head; 21 if(runner.next == null) 22 return null; 23 while(runner.next.next != null) 24 runner = runner.next; 25 runner.next = null; 26 return head; 27 } 28 29 ListNode fastrunner = head; 30 ListNode slowrunner = head; 31 while(n > 0) 32 { 33 fastrunner = fastrunner.next; 34 n--; 35 if(fastrunner == null) 36 { 37 return head.next; 38 } 39 } 40 while(fastrunner.next != null) 41 { 42 slowrunner = slowrunner.next; 43 fastrunner = fastrunner.next; 44 } 45 slowrunner.next = slowrunner.next.next; 46 return head; 47 } 48 }
