Compute root-to-leaf number sum
Company: Bytedance
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
Given the root of a binary tree where each node stores a digit from `0` to `9`, every root-to-leaf path represents a decimal number formed by concatenating the digits along the path.
Return the sum of all numbers represented by every root-to-leaf path.
A leaf is a node with no children.
Example:
- Input tree: `[4,9,0,5,1]`
- Root-to-leaf numbers: `495`, `491`, and `40`
- Output: `1026`
Function signature (language-agnostic):
`int sumRootToLeafNumbers(TreeNode root)`
Constraints:
- The number of nodes is in the range `[0, 1000]`.
- `0 <= node.val <= 9`.
Quick Answer: This question evaluates understanding of binary tree data structures and the competency to aggregate values along root-to-leaf paths, combining tree traversal with numeric accumulation of node digits.
Given level-order digit tree values, sum all root-to-leaf numbers.
Constraints
- Inputs are Python literals matching the function signature.
- Return a deterministic exact-match value.
Examples
Input: ([4,9,0,5,1],)
Expected Output: 1026
Explanation: Prompt example.
Input: ([],)
Expected Output: 0
Explanation: Empty tree.
Input: ([1,2,3],)
Expected Output: 25
Explanation: Two root-leaf numbers.
Hints
- Model object-style prompts as operation streams when needed.
- Handle empty and boundary cases before the main logic.