Sum numbers formed by root-to-leaf paths

Q: Sum numbers formed by root-to-leaf paths

This question evaluates a candidate's ability to work with binary tree traversal and path-based numerical aggregation, testing competency in tree data structures and algorithmic reasoning within the Coding & Algorithms domain.

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Question

You are given the root of a binary tree where each node contains a single digit from 0 to 9.

Each root-to-leaf path represents a number obtained by concatenating the digits along the path from the root down to a leaf. For example, if a path is root → 1 → 2 → 3, it represents the number 123.

Write a function that returns the sum of all numbers formed by all root-to-leaf paths in the tree.

Input: the root node of a binary tree.
Output: an integer representing the sum of all root-to-leaf numbers.

Constraints:

Each node value is a digit from 0 to 9.
The tree has at most 1000 nodes.

Describe your algorithm and its time and space complexity. You do not need to provide actual code.

Sum numbers formed by root-to-leaf paths

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