Interview Questions

1. Binary Tree Level Order Traversal

   coding

   Practice

   Title: Binary Tree Level Order Traversal

   Problem: Given the root of a binary tree, return the level order traversal of its node values. (i.e., from left to right, level by level).

   Function Signature: def level_order(root: Optional[TreeNode]) -> List[List[int]]:

   Input: root: Optional[TreeNode] — the root node of a binary tree

   Output: A list of lists of integers representing values at each level from top to bottom

   Sample Input: [3, 9, 20, null, null, 15, 7]

   Sample Output: [[3], [9, 20], [15, 7]]

   Example: For the binary tree: 3 / \ 9 20 /
   15 7 The level order traversal returns [[3], [9, 20], [15, 7]].

   Constraints: The number of nodes in the tree is in the range [0, 2000]. -1000 ≤ Node.val ≤ 1000.

   Hints: Use a queue (breadth-first search) to process each node level by level. Enqueue the children of each node as you go.

   Follow-up: Can you solve it using recursion? How would you return the level order traversal from bottom to top (reverse level order)?