Compute subtree sums with tree DFS

Q: Compute subtree sums with tree DFS

This question evaluates proficiency in tree traversal and aggregation techniques, specifically computing subtree sums using depth-first search while handling traversal state and constraints such as negative values and large n.

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Question

You are given an undirected tree with n nodes labeled 1..n and n-1 edges. The tree is rooted at node 1. Each node i has an integer value val[i].

Return an array subtreeSum[1..n] where subtreeSum[u] is the sum of val[x] over all nodes x in the subtree of u (including u).

Constraints:

1 <= n <= 2e5
Values can be negative.
The input is guaranteed to be a tree.

Implement an O(n) solution using DFS.

Compute subtree sums with tree DFS

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