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0328-odd-even-linked-list/0328-odd-even-linked-list.py

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+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def oddEvenList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        """
+        Complexities:
+        Time:  O(n)
+        Space: O(1)
+
+        where n = len(head)
+        """
+
+        # If len(head) <= 2, already sorted
+        if not head or not head.next:
+            return head
+
+        oddHead = head
+        oddTail = head
+        evenHead = head.next
+        evenTail = head.next
+
+        currNode = head.next.next
+        isOddIndex = True
+
+        # Set tail.next = None
+        oddTail.next = None
+        evenTail.next = None
+
+        # Separate list into odd list and even list
+        while currNode:
+            nextNode = currNode.next
+            currNode.next = None
+
+            if isOddIndex:
+                oddTail.next = currNode
+                oddTail = currNode
+            else:
+                evenTail.next = currNode
+                evenTail = currNode
+            
+            currNode = nextNode
+            isOddIndex = not isOddIndex
+
+        # Attach both lists
+        oddTail.next = evenHead
+
+        return oddHead