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Try the Capturing Rainwater interview problem.

Capturing Rainwater

Create a `capturing_rainwater()` function that takes in an array of heights, and returns the amount of rainwater that could be contained in that array. 

For example, the array `[4, 2, 1, 3, 0, 1, 2]` can be represented in the following histogram:
<img src="https://static-assets.codecademy.com/curriculum/code-challenges/Image 2.svg" alt="Histogram with the Y-axis going from 0 to 4 and the X-axis containing the numbers from the array. Water is pooled in the empty spaces of the histogram, and you can see that it can contain 6 units of water."/>
As you can see, there are 6 units of water that can be contained, so `capturing_rainwater([4, 2, 1, 3, 0, 1, 2])` will return `6`.

This challenge was reported to have been asked at interviews with many top companies, including Amazon and Microsoft. If you've covered the material in [Pass the Technical Interview with Python](https://www.codecademy.com/learn/paths/pass-the-technical-interview-with-python) or an equivalent, you should be able to solve this challenge. If you have trouble, try refreshing your knowledge with its [Capturing Rainwater](https://www.codecademy.com/paths/pass-the-technical-interview-with-python/tracks/interview-prep-and-practice/modules/python-interview-problems/articles/capturing-rainwater-python-article) walkthrough.