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0103-binary-tree-zigzag-level-order-traversal/0103-binary-tree-zigzag-level-order-traversal.py

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+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def zigzagLevelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+        """
+        Complexities:
+        Time:  O(n)
+        Space: O(n)
+
+        where n = number of nodes in graph
+        """
+
+        if not root:
+            return []
+
+        traversal = [[root]]
+        hasNextLevel = root.left or root.right
+
+
+        # Store nodes from left to right in arrays by depth - O(n)
+        while hasNextLevel:
+            lastLevel = traversal[-1]
+            nextLevel = []
+            hasNextLevel = False
+
+            for node in lastLevel:
+                if node.left:
+                    nextLevel.append(node.left)
+                    hasNextLevel = hasNextLevel or bool(node.left.left or node.left.right)
+                
+                if node.right:
+                    nextLevel.append(node.right)
+                    hasNextLevel = hasNextLevel or bool(node.right.left or node.right.right)
+
+            traversal.append(nextLevel)
+
+        # Convert nodes to values + reverse every other level - O(n)
+        valueTraversal = []
+        for depth, level in enumerate(traversal):
+            start = 0 if depth % 2 == 0 else len(level) - 1
+            end = len(level) if depth % 2 == 0 else -1
+            step = 1 if depth % 2 == 0 else -1
+
+            nextLevelValues = []
+            for i in range(start, end, step):
+                nextLevelValues.append(level[i].val)
+            valueTraversal.append(nextLevelValues)
+                
+
+
+        return valueTraversal
+            
+
+