Easy data structure and algorithm practice puzzle.
Given n, return the sum of every whole number from 1 to n. A loop works. Gauss's trick is faster: pair 1 with n, 2 with n - 1, and so on. Every pair adds up to n + 1, and there are n / 2 pairs, so the answer is n(n + 1) / 2. No loop at all.
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 Reading Smoothing Rig, a pipeline you can run and download. See every Software Engineer project.
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