- Reorder List #247

Author: ayosecu

reorder-list/ayosecu.py

@@ -0,0 +1,61 @@
+from typing import Optional
+from collections import deque
+
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+class Solution:
+    """
+        - Time Complexity: O(N), N = The number of nodes.
+        - Space Complexity: O(N)
+    """
+    def reorderList(self, head: Optional[ListNode]) -> None:
+        dq = deque()
+
+        cur = head
+        while cur:
+            dq.append(cur)
+            cur = cur.next
+        
+        dummy = ListNode(-1)
+        cur = dummy
+        flag = True
+        while dq:
+            if flag:
+                cur.next = dq.popleft()
+            else:
+                cur.next = dq.pop()
+            cur = cur.next
+            flag = not flag
+        cur.next = None
+
+        return dummy.next
+
+### TC Helpers ###
+def build_linked_list(values):
+    dummy = ListNode(0)
+    current = dummy
+    for v in values:
+        current.next = ListNode(v)
+        current = current.next
+    return dummy.next
+
+def linked_list_to_list(head):
+    result = []
+    while head:
+        result.append(head.val)
+        head = head.next
+    return result
+
+### TC ###
+tc = [
+        ([1,2,3,4], [1,4,2,3]),
+        ([1,2,3,4,5], [1,5,2,4,3])
+]
+
+sol = Solution()
+for i, (l, e) in enumerate(tc, 1):
+    r = linked_list_to_list(sol.reorderList(build_linked_list(l)))
+    print(f"TC {i} is Passed!" if r == e else f"TC {i} is Failed! - Expected: {e}, Result: {r}")