Bottom-up Fisher-Yates

The Fisher-Yates implementation on the previous slide goes “top down”, i.e., it starts at index n-1 and counts down. Write another version that counts up. Wikipedia has pseudocode for you:

-- To shuffle an array a of n elements (indices 0..n-1):
for i from 0 to n−2 do
    j ← random integer such that i ≤ j < n
    exchange a[i] and a[j]

Write some tests to convince yourself you got it right; the ‘Mark’ button just runs doctest (and so will be green if you don’t write any, whether or not your code works!).