Determine the shuffled indices of two lists/arrays

Question

As a challenge, I\'ve given myself this problem:

Given 2 lists, A, and B, where B is a shuffled version of A, the idea is to figure out the shuffled indices.

Answer 1

As mentioned in my question, I was able to solve this using a dictionary. I store the indices in a dict and then use a list comprehension to pop them out:

A = [10, 40, 30, 2]
B = [30, 2, 10, 40]

idx = {}
for i, l in enumerate(A):
    idx.setdefault(l, []).append(i)

res = [idx[l].pop() for l in B]
print(res)

Output:

[2, 3, 0, 1]

This is better than the obvious [A.index(x) for x in B] because it is

1. linear
2. handles duplicates gracefully