leetcode 19 Remove n-th Node from End of List
z
 2018-03-01 22:03:56  

Given a linked list, remove the nth node from the end of list and return its head.

For example,

1
2
3
4
Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5.

Note:
Given n will always be valid.
Try to do this in one pass.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode slow = head;
        ListNode fast = head;
        int i = 0;
        while(i!=n){
            fast = fast.next;
            i++;
        }
        if(fast == null){
            return slow.next;
        }
        while(fast.next != null){
            fast = fast.next;
            slow = slow.next;
        }
        slow.next = slow.next.next;
        return head;
    }
    
}
  • Using two points, both starts with pointing to the first node.
  • Moving the fast pointer n times, so that fast is n nodes ahead the slow pointer
  • Moving the two pointers in the same time untile fast reaches the end of the linked list
  • Notice that when there is only one node in the list and removing the only element. This is an special case which need to be examed.