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Deven
68 lines
1.7 KiB
Python
68 lines
1.7 KiB
Python
# 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 reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
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if k == 1:
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return head
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dummyHead = ListNode(-1, head)
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beforeSeg = dummyHead
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firstInSeg = head
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lastInSeg = None
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afterSeg = None
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# Get initial values for lastInSeg and afterSeg
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curr = head
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for i in range(k):
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if i == k - 1:
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lastInSeg = curr
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afterSeg = curr.next
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elif curr is None:
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return head
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curr = curr.next
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# hold one before segment
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# hold last in segment
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# hold one after segment
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while lastInSeg is not None:
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# in segment, flip all links
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prev = None
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curr = beforeSeg.next
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next = beforeSeg.next.next
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for i in range(k):
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newPrev = curr
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newCurr = next
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newNext = next.next if next is not None else None
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curr.next = prev
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prev, curr, next = newPrev, newCurr, newNext
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beforeSeg.next = lastInSeg
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firstInSeg.next = afterSeg
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beforeSeg = firstInSeg
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firstInSeg = afterSeg
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curr = firstInSeg
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lastInSeg = None
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afterSeg = None
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for i in range(k):
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if curr is None:
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break
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elif i == k - 1:
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lastInSeg = curr
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afterSeg = curr.next
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curr = curr.next
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return dummyHead.next |