"""
19. Remove Nth Node From End of List
Medium

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

Follow up: Could you do this in one pass?

 

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

https://leetcode.com/problems/remove-nth-node-from-end-of-list/
"""

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
        root = ListNode(-1, head)
        ptr = root
        delay = 0 - n
        while head.next:
            head = head.next
            delay += 1
            if delay >= 0:
                ptr = ptr.next
        ptr.next = ptr.next.next
        return root.next
