Binary Tree Zigzag Level Order Traversal with step by step explanation
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\nTo traverse the binary tree in a zigzag manner, we can use a breadth-firs
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\nTo traverse the binary tree in a zigzag manner, we can use a breadth-first search (BFS) approach. We can use a queue to store the nodes of the binary tree, and we can use a flag to indicate the direction of the zigzag traversal.\n\nIf the flag is set to left-to-right, we can append the node values from left to right to the current level list. Otherwise, if the flag is set to right-to-left, we can append the node values from right to left to the current level list.\n\nOnce we have appended all the node values for the current level, we can update the flag to switch the direction of the zigzag traversal and append the current level list to the result list.\n\n# Complexity\n- Time complexity:\nThe time complexity of this solution is O(N), where N is the number of nodes in the binary tree, since we need to traverse all the nodes. \n\n- Space complexity:\nThe space complexity of this solution is O(N), since we need to store all the nodes in the queue.\n\n# Code\nHere is the Python3 code with comments explaining each step:\n```\nclass Solution:\n    def zigzagLevelOrder(self, root: TreeNode) -> List[List[int]]:\n        if not root:\n            return []\n        \n        # Initialize the queue with the root node\n        queue = [root]\n        \n        # Initialize the flag to indicate the direction of the zigzag traversal\n        is_left_to_right = True\n        \n        # Initialize the result list\n        result = []\n        \n        while queue:\n            # Initialize the current level list\n            level = []\n            \n            # Get the size of the current level\n            size = len(queue)\n            \n            for i in range(size):\n                # Remove the first node from the queue\n                node = queue.pop(0)\n                \n                # Append the node value to the current level list\n                level.append(node.val)\n                \n                # Add the left and right children of the node to the queue\n                if node.left:\n                    queue.append(node.left)\n                if node.right:\n                    queue.append(node.right)\n            \n            # Update the flag to switch the direction of the zigzag traversal\n            if is_left_to_right:\n                is_left_to_right = False\n            else:\n                is_left_to_right = True\n                level = level[::-1]  # Reverse the current level list if the flag is set to right-to-left\n            \n            # Append the current level list to the result list\n            result.append(level)\n        \n        return result\n\n```
['Tree', 'Breadth-First Search', 'Binary Tree', 'Python', 'Python3']