26 lines
762 B
Python
26 lines
762 B
Python
# Time: O(N)
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# Space: O(1)
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class Solution:
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def swapNodes(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
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# We are using two pointer approach here
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kth_node = kth_end_node = None
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n = 1
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ptr = head
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while ptr != None:
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if n == k:
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kth_node = ptr
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# `kth_end_node` ptr will only start moving once
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# we've traversed k nodes from the beginning of the
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# linked list
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if n >= k:
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kth_end_node = head if kth_end_node is None else kth_end_node.next
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n += 1
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ptr = ptr.next
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kth_node.val, kth_end_node.val = kth_end_node.val, kth_node.val
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return head
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