Reorder List

0143-Reorder-List.py

@@ -0,0 +1,44 @@
+'''
+Given a singly linked list L: L0→L1→…→Ln-1→Ln,
+reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…
+
+You may not modify the values in the list's nodes, only nodes itself may be changed.
+
+Example 1:
+
+Given 1->2->3->4, reorder it to 1->4->2->3.
+Example 2:
+
+Given 1->2->3->4->5, reorder it to 1->5->2->4->3.
+'''
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution:
+    def reorderList(self, head: ListNode) -> None:
+        """
+        Do not return anything, modify head in-place instead.
+        """
+        if not head:
+            return
+
+        slow = fast = head
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+
+        last = None
+        while slow:
+            slow.next, last, slow = last, slow, slow.next
+
+        cur = head
+        while last.next:            
+            cur_next = cur.next
+            last_next = last.next
+            cur.next = last
+            cur = cur_next
+            last.next = cur
+            last = last_next