不了解中位数算法的中位数来找到第k个元素

Below is my code for trying to understand the median of medians algorithm (using blocks of size 5). I understand how to get medians of the input, but I'm not sure how to code the block to keep recursing the input until I just have the median. Then after getting that median, I'm not sure how to use it as a pivot to throw away the useless information to partition the input. Below is my code for trying to understand the m