19 Remove Nth Node From End of List

🔀 Pick One

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

Example 1:

1 -> 2 -> 3 -> (4) -> 5

1 -> 2 -> 3 --------> 5

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?

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# 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]:
        dummy = ListNode(0, head)
        fast = slow = dummy
        for i in range(n+1):
            fast = fast.next

        while fast:
            fast = fast.next
            slow = slow.next

        slow.next = slow.next.next
        return dummy.next