← Bytedance Interview Insights
This is basically LeetCode 437 but with an N-ary tree instead of a binary one.
Use a depth-first traversal while maintaining a prefix sum map to count paths that sum to the target. At each node, compute the current prefix sum and check how many times (current sum - target) has occurred in the map, then add the current sum to the map before recursing into children and remove it after backtracking.
Pro tip: Clarify that the path must go downwards (parent to child) and mention that the prefix sum map approach is optimal for this problem, avoiding the O(N^2) brute-force method. Also, discuss how to handle large trees and potential integer overflow.
Confirm that paths must go downwards (from ancestor to descendant) and that the tree can be large, so an efficient solution is needed. Ask about the range of node values and target to handle potential overflow.
Select depth-first search (DFS) for traversal and a hash map to store prefix sums and their frequencies. This allows O(1) lookups for the required complement.
Write a DFS function that takes the current node, the current prefix sum, and the prefix sum map. At each node, update the prefix sum and check for paths ending at this node.
After processing the current node, recurse into all children, then remove the current prefix sum from the map to ensure it only reflects the current path.
State that time complexity is O(N) and space is O(N) for the map and recursion stack. Discuss edge cases like empty tree, target zero, and negative values.
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