Split Array with Equal Sum
A hard-tier problem at 50% community acceptance, tagged with Array, Hash Table, Prefix Sum. Reported in interviews at Alibaba and 0 others.
Split Array with Equal Sum is a 50% acceptance rate problem that Alibaba consistently asks. You're given an array and need to find a way to partition it so that multiple segments have equal sums. The trap: the obvious brute-force approach of checking every possible split point will time out. Candidates often miss the constraint structure or don't recognize when a hash table can collapse O(n^2) down to linear work. If this problem hits your live assessment and you freeze on the pattern, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Split Array with Equal Sum"
Split Array with Equal Sum 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 FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know.
Get StealthCoderThe core insight is prefix sums plus hash tables. Precompute cumulative sums across the array, then recognize that equal segments mean you're looking for repeated prefix differences. The temptation is to loop through every potential split point and verify each one independently, which explodes the time complexity. Instead, store seen prefix sums in a hash table and check if the current prefix sum minus a target sum already exists. This converts the problem from nested loops into a single pass. Common pitfall: forgetting that segments must not overlap or include the entire array. Candidates who drill on prefix sum problems but skip hash table optimization usually hit a wall here. On an actual assessment, StealthCoder bridges that gap by showing you the hash table pattern applied to this exact structure.
Pattern tags
You know the problem.
Make sure you actually pass it.
Split Array with Equal Sum recycles across companies for a reason. It's hard-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 FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Split Array with Equal Sum interview FAQ
Is this really hard or is the 50% acceptance just difficulty inflation?+
It's legitimately hard. The 50% acceptance reflects that most candidates either brute-force it and time out or don't see the prefix sum plus hash table combo. Once you know the pattern, it's medium. Cold read? Very hard. That's where the acceptance rate sits.
How does prefix sum connect to hash table here?+
Prefix sum tells you segment totals without recomputing. Hash table stores which sums you've already seen. If you see the same prefix sum value twice, the segment between them has sum zero. If you see a difference of your target sum in the table, you've found a valid segment. Hash table makes lookups O(1) instead of rescanning.
Why do candidates fail this at Alibaba?+
Most don't realize the naive split-and-verify approach is too slow. They also miss that equal sum segments have a constraint structure you can exploit with one data structure. The problem looks array-heavy but it's actually testing hash table intuition under time pressure.
What's the main gotcha to watch?+
Segments must be non-overlapping and usually can't include the whole array. Read the problem statement carefully for edge cases like empty segments or whether partition indices matter. Off-by-one errors in boundary checks are common when you're rushing.
Should I memorize this or understand the pattern?+
Understand the pattern. This is a specific instance of prefix sum optimization with hash tables. Once you've done it once, you'll see it in other partition or subarray problems. Memorizing the solution burns out on variants during the live OA.
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