LeetCode #102 - Binary Tree Level Order Traversal: Given a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level). Example Input: root = [3,9,20,null,null,15,7] Example Output: [[3],[9,20],[15,7]] Constraints: The number of nodes in the tree is in the range [0, 2000]. -1000 <= Node.val <= 1000.

``` ## Approach To traverse the tree level by level, a breadth-first search (BFS) approach is suitable. We can utilize a queue to keep track of nodes at the current level. Each time we process a node, we add its children to the queue for the next level. ## Complexity **Time:** O(N) where N is the number of nodes in the tree. **Space:** O(W) where W is the maximum width of the tree at any level. ## Trade-offs - BFS is straightforward but requires extra space for the queue. ```