Hard data structure and algorithm practice puzzle.
Given a list of numbers, return true if you can split them into two groups with equal sums. If the total is odd, it's impossible. Otherwise, the question is whether some of the numbers add up to exactly half the total. Recurse through the numbers, trying each one in and out of that half.
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 Ranking Service, a pipeline you can run and download. See every Software Engineer project.
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