You'll learn the prefix accumulation pattern that appears in harder problems like Product Except Self, Subarray Sum Equals K, and Range Sum Query. If you can't build a prefix sum array, you'll write solutions where exists. The prefix pattern lets you answer range queries in after preprocessing. Google, Amazon, and Meta all ask prefix sum variations.
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$ curl repovive.com/roadmaps/maang-interview-prep/arrays-hashing/running-sum-why-this-problem
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