# Remove Nth Node From End of List
###### tags: `Medium` `Linked List`
>question : https://leetcode.com/explore/interview/card/top-interview-questions-easy/93/linked-list/603/

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        int length  = 0;
        ListNode first = head;
        while (first != null) {
            length++;
            first = first.next;
        }
        length -= n;
        first = dummy;
        while (length > 0) {
            length--;
            first = first.next;
        }
        first.next = first.next.next;
        return dummy.next;
    }
}

- python
分別用兩個指標，fast指向最後，slow指向與fast距離n的位置，即要刪除的節點

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def removeNthFromEnd(self, head, n):
        """
        :type head: ListNode
        :type n: int
        :rtype: ListNode
        """
        slow = fast = head
        while n > 0:
            fast = fast.next
            n -= 1
        
        if fast == None:
            head = head.next
            return head
    
        while fast.next != None:
            slow = slow.next
            fast = fast.next
        
        slow.next = slow.next.next #刪除第n個節點
        return head