19. Remove Nth Node From End of List【Medium】【删除单链表倒数第n个结点】

/**
 * 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) {
        if(head == null) return null;
        ListNode fast = head;
        while(n-- > 0) {
            fast = fast.next;
        }
        if(fast == null) return head.next;
        ListNode slow = head;
        while(fast.next != null) {
            slow = slow.next;
            fast = fast.next;
        }
        slow.next = slow.next.next;
        return head;
    }
}