19. Remove Nth Node From End of List

Problem

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

Example 1:

Input: head = [1,2,3,4,5], n = 2
Output: [1,2,3,5]

Example 2:

Input: head = [1], n = 1
Output: []

Example 3:

Input: head = [1,2], n = 1
Output: [1]

Constraints:

• The number of nodes in the list is sz.
• 1 <= sz <= 30
• 0 <= Node.val <= 100
• 1 <= n <= sz

双指针，维持两者之间的距离在n，这样第二个指针走到尽头的时候，第一个刚好跟尽头相差n

class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode first = dummy;
        ListNode second = dummy;
 
        for(int i = 0; i <= n; i++){
            first = first.next;
        }
 
        while(first != null){
            first = first.next;
            second = second.next;
        }
 
        second.next = second.next.next;
        return dummy.next;
    }
}