LeetCode #19 Remove Nth Node From End of List (E)

[Problem]

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

For example,

   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.

 

[Analysis]

用固定距离的double pointer解决。

 

[Solution]

public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        int i = 1;
        ListNode node = head;
        ListNode pre = new ListNode(0);
        pre.next = head;
        
        while (node.next != null) {
            node = node.next;            
            if (++i > n) {
                pre = pre.next;
            }
        }        
        
        if (pre.next == head) {
            return head.next;
        }
        
        pre.next = pre.next.next;
        return head;
    }
}