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# Runtime: 65 ms (Top 20.14%) | Memory: 13.9 MB (Top 70.35%)
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# Definition for singly-linked list.
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# class ListNode:
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# def __init__(self, val=0, next=None):
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# self.val = val
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# self.next = next
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class Solution:
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    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
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        if head == None:
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            return None
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        slow = head
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        fast = head
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        for i in range(n):
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            fast = fast.next
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        if fast == None:
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            return head.next
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        while fast != None and fast.next != None:
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            slow = slow.next
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            fast = fast.next
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        slow.next = slow.next.next
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        return head