WRITE · TRACE · UNDERSTAND
Prefix Sums
Build cumulative totals, then answer ranges with two lookups
Your experiment
range_sums(values, queries) returns sums for half-open ranges [left, right). Build a prefix table once, then watch each query cancel the part before left.
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What to look for
prefix[i] is the total before i. The extra zero handles ranges beginning at zero and empty ranges. Trace the table being built, then compare the two boundaries for each query.
Watch your code work
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