Look for these signals in the problem:
- "Sum of subarray/range" queries: Precompute prefix sums for range sum queries.
- "Subarray sum equals k": Use hash map to track prefix sums seen; find complements.
- "Count subarrays" with sum property: Prefix sum + hash map counts subarrays efficiently.
- "2D range sum" queries: Extend prefix sum to 2D with inclusion-exclusion.
- "Product except self": Prefix and suffix products avoid division issues.