This question evaluates a candidate's competence in binary tree data structures and algorithmic efficiency, focusing on tree traversal techniques, subtree aggregation, and handling robustness aspects such as empty trees and integer overflow.
Given the roots of two complete binary trees T1 and T2 that have identical structure and the same number of nodes, replace each value in T2 with the sum of all node values in the corresponding subtree of T1 (including the matching root of that subtree). Implement: (