Range Addition
A medium-tier problem at 72% community acceptance, tagged with Array, Prefix Sum. Reported in interviews at Salesforce and 0 others.
Range Addition shows up in Salesforce's online assessments and catches candidates off guard because the naive approach tanks on performance. You're given an empty array and a list of range operations (add value X to indices L through R). The trap is simulating each operation directly, which times out on large arrays. This is a prefix sum problem disguised as a range update problem. The real solution uses a difference array to batch operations in O(1) per update, then reconstruct the final array in a single pass. If you hit this live and freeze on optimization, StealthCoder solves it invisibly and surfaces the pattern in seconds.
Companies that ask "Range Addition"
Range Addition is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Made by a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE.
Get StealthCoderThe key insight: don't update the range itself. Instead, mark the boundaries. Store +value at index L and -value at index R+1. After all operations, run a prefix sum scan across the difference array to get final values. This drops you from O(n*m) (where m is operation count) to O(n+m), which is the difference between timing out and passing. Most candidates lock onto the simulation approach and don't realize the difference array trick until they see the time limit exceeded. The problem tests whether you recognize that prefix sum isn't just about computing cumulative sums, it's a tool for batching range updates. StealthCoder is your safety net if you blank on the optimization during the actual assessment.
Pattern tags
You know the problem.
Make sure you actually pass it.
Range Addition recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Made by a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Range Addition interview FAQ
Why does the direct simulation approach fail?+
Direct simulation iterates through the entire range L to R for each operation. With a large array (10^5 elements) and many operations (10^4), you're doing 10^9 operations. The difference array does each operation in O(1) instead, reducing total time from O(n*m) to O(n+m). That's the difference between timeout and acceptance.
Is Range Addition still asked at Salesforce?+
Yes, Salesforce includes it in their reported assessments. With a 72% acceptance rate, it's not trivial but very solvable once you internalize the difference array pattern. The problem is designed to test optimization thinking, not just correctness.
How does the difference array actually work for range updates?+
Mark the start and end of each range: increment at L, decrement at R+1. When you scan left-to-right with a running sum, the cumulative effect applies the value to exactly the range L to R. No loop needed per operation. It's elegant once you see it.
What's the relationship between this problem and prefix sums?+
Prefix sums are typically used to answer range-query questions fast. Here, they solve the inverse problem: apply range updates fast. The difference array is the inverse operation. Understanding both directions is critical for array problems at this level.
Can I solve Range Addition without the difference array trick?+
Technically yes, but you'll likely fail performance tests. The difference array is not an optional optimization; it's the intended solution. If you can't recall it under pressure, that's exactly when StealthCoder helps you avoid a rejected submission.
Want the actual problem statement? View "Range Addition" on LeetCode →