Running sum of daily signups

Python data engineering interview problem. Difficulty: beginner. Pattern: Aggregation. About 10 minutes. Part of the Pro drill bank.

Growth tracks daily new signups. Finance wants a running total so day 3's number is signups from day 1 through day 3, not that day alone.

Turn a list of daily signup counts into a prefix (running) sum.

Requirements

• Each output index i is the sum of daily[0] through daily[i].
• Preserve list length.

Constraints

• daily: list of non-negative daily counts.

Examples

Input: running_sum([1, 2, 3]) Output: [1, 3, 6] This input follows the stated rules and produces this output.

Topics: lakebench, python, iteration.

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