Medium data structure and algorithm practice puzzle.
Given a discount rate and a list of yearly cash flows, starting with year 0, return the net present value, rounded to 2 decimals. Divide each year's flow by (1 + rate) to the power of its year, then add them all up. Year 0 is divided by 1, so it counts in full. Money later is worth less than money now.
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 Trade Forecaster, a pipeline you can run and download. See every Software Engineer project.
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