Time: 61 ms (99.71%), Space: 26.3 MB (15.45%) - LeetHub

Author: snowphone

0143-reorder-list/0143-reorder-list.py

@@ -0,0 +1,47 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def middle(self, head):
+        prev = ListNode(0, head)
+        slow = head; fast = head
+        while fast:
+            prev, slow = slow, slow.next
+            try:
+                fast = fast.next.next
+            except:
+                break
+        prev.next = None
+        return slow
+    
+    def rev(self, head):
+        prev = None
+        nd = head
+        while nd:
+            nxt = nd.next
+            nd.next = prev
+            prev, nd = nd, nxt
+        return prev
+    
+    def reorderList(self, head: Optional[ListNode]) -> None:
+        """
+        Do not return anything, modify head in-place instead.
+        """
+        mid = self.middle(head)
+        revhead = self.rev(mid)
+        dummy = ListNode(); tail = dummy
+
+        while head and revhead:
+            tail.next = head
+            tail = tail.next
+            head = head.next
+
+            tail.next = revhead
+            tail = tail.next
+            revhead = revhead.next
+
+        if head:
+            tail.next = head
+