Serialize and Deserialize Binary Tree (Preorder)

To solve this, I would use a Preorder traversal approach where we visit the root first, then the left subtree, and finally the right subtree. For serialization, I'll convert each node value to a string. If a node is null, I will append a specific marker, say '#', separated by commas. This creates a unique sequence representing the tree structure. For example, a tree with root 1, left child 2, and right child 3 becomes '1,2,#,#,3,#,#'. For deserialization, I will split the input string by commas to create a queue or list of tokens. I'll use a recursive helper function that consumes the front token from the list. If the token is '#', we return null. Otherwise, we create a new TreeNode with the integer value, then recursively call the function to build its left child, followed immediately by the right child. Since the order matches our serialization, the recursion naturally reconstructs the original hierarchy. This approach ensures O(N) time complexity because we visit every node exactly once during both processes. The space complexity is O(N) for storing the string and the recursion stack, which is optimal. I would also add a check for an empty input string to return null immediately, ensuring robustness against edge cases.