Reverse Nodes in k-Group
Reverse nodes in k-group in a linked list.
Input: head = [1,2,3,4,5], k = 3
Output: [3,2,1,4,5]
Explanation: The first 3 elements are reversed, while the remaining 2 are left untouched since they don't form a complete group.

Question

Reverse Nodes in k-Group

Reverse nodes in k-group in a linked list.

Input: head = [1,2,3,4,5], k = 3

Output: [3,2,1,4,5]

Explanation: The first 3 elements are reversed, while the remaining 2 are left untouched since they don't form a complete group.

Anonymous · Accepted Answer

def reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:

def reverse(node: Optional[ListNode]) -> Optional[ListNode]:
            if not node:
                return None
            prev, curr = None, node
            while curr:
                temp = curr.next
                curr.next = prev
                prev, curr = curr, temp
            return prev
        
        dummy = ListNode(0, head)
        tail, runner = dummy, head
        counter = 1

while runner:
            if counter == k:
                next_node, next_tail = runner.next, tail.next
                runner.next = None

new_head = reverse(tail.next)
                tail.next = new_head
                tail, runner = next_tail, next_node
                tail.next = runner

counter = 1
            else:
                counter += 1
                runner = runner.next
        
        return dummy.next

Reverse Nodes in k-Group

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