Medium data structure and algorithm practice puzzle.
A production line logs its output once an hour. Given the hourly output and a list of shifts as [firstHour, lastHour], both included, return the total output for each shift. There can be lots of shifts, so re-adding the hours for every one is too slow. Do some work up front so each shift's total takes one step.
Solve it three ways: snap the jigsaw pieces together, fill in the blanks, or type it from scratch against the tests. This one is free.
Every line of the solution comes with a note explaining why it is there, and a step by step replay shows the code running. At level 3, where you type it yourself, you can ask for an AI mock interview on this problem that ends with a hiring manager's scorecard.
Then grow it into a real project with the Software Engineer button: this puzzle becomes the Order Throughput Report, a pipeline you can run and download. See every Software Engineer project.
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