19. Remove Nth Node From End of List

Medium

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Given the head of a linked list, remove the nth 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

Follow up: Could you do this in one pass?

# 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: Optional[ListNode], n: int) -> Optional[ListNode]:
        slow, fast = head, head
        for _ in range(n):
            fast = fast.next
        if not fast:
            return slow.next
        while fast.next:
            slow = slow.next
            fast = fast.next
        slow.next = slow.next.next
        return head