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Which of the following changes to the DFS approach is necessary to handle this correctly?

hard🎤 Interviewer Follow-up Q15 of Q15
Tree: Depth-First Search - Path Sum
Suppose the Path Sum problem is modified so that node values can be negative, and you want to find if any root-to-leaf path sums exactly to targetSum. Which of the following changes to the DFS approach is necessary to handle this correctly?
APrecompute all path sums and store them in a hash set for O(1) lookup
BAdd memoization to avoid revisiting nodes with the same current sum
CUse BFS instead of DFS to guarantee shortest path sum
DRemove early stopping because negative values can invalidate pruning assumptions
Step-by-Step Solution

  1. Step 1: Understand impact of negative values

    Negative values mean partial sums can decrease later, so pruning based on current sum is unsafe.

  2. Step 2: Adjust algorithm accordingly

    Early stopping based on partial sums must be removed to avoid missing valid paths.

  3. Final Answer:

    Option D -> Option D

  4. Quick Check:

    Negative values break pruning assumptions, so early stopping must be disabled [OK]
Quick Trick: Negative values invalidate pruning, so no early stopping [OK]
Common Mistakes:
MISTAKES
  • Assuming early stopping always works
  • Switching to BFS unnecessarily
Trap Explanation:
PITFALL
  • Early stopping looks efficient but fails with negative values; memoization or BFS don't solve pruning issues here.
Interviewer Note:
CONTEXT
  • Tests candidate's understanding of pruning assumptions and algorithm robustness.
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