Medium data structure and algorithm practice puzzle.
Given a list of numbers, apply the GELU activation to each one and return the results, rounded to 4 decimals. Use the tanh version: 0.5 x (1 + tanh(sqrt(2 / pi) x (x + 0.044715 x cubed))). Unlike ReLU, GELU is smooth and lets small negative values through, so a neuron that dips below 0 can still recover.
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 Sample Stats Roll-up, a pipeline you can run and download. See every Software Engineer project.
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