Given a matrix x with n rows and m columns, return a matrix y with 2n rows and m columns, such that every column in x is sorted from low to high and then from high to low.
Example:
x = 8 9 3 9
9 6 5 2
2 1 9 9
y = 2 1 3 2
8 6 5 9
9 9 9 9
9 9 9 9
8 6 5 9
2 1 3 2
Additional test cases have been added.