328_odd_even_linked_list.py

class Solution:
    def oddEvenList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        if not head:
            return head

        odd = head
        even = head.next
        even_head = even

        while even and even.next:
            odd.next = even.next
            odd = odd.next
            even.next = odd.next
            even = even.next

        odd.next = even_head
        return head
        
        # Time Complexity O(n)
        # Space Complexity O(1)