Mathematical explanation of Leetcode question: Container With Most Water

I was working on a medium level leetcode question 11. Container With Most Water. Besides the brute force solution with O(n^2), there is an optimal solution with complexity of O(n) by using two pointers from left and right side of the container. I am a little bit confused why this “two pointers” method must include the optimal solution. Does anyone know how to prove the correctness of this algorithm mathematically? This is an algorithm that I don’t know of. Thank you!

Rolling or sliding window iterator?

I need a rolling window (aka sliding window) iterable over a sequence/iterator/generator. Default Python iteration can be considered a special case, where the window length is 1. I’m currently using the following code. Does anyone have a more Pythonic, less verbose, or more efficient method for doing this?