Inverting permutations in Python

Question

I\'m new to programming, and I\'m trying to write a Python function to find the inverse of a permutation on {1,2,3,...,n} using the following code:

def inv(s         


        

Answer 1

A "functional style" version:

def invert_permutation(permutation):
    return [i for i, j in sorted(enumerate(permutation), key=lambda (_, j): j)]

Basically, sorting the indices i of the permutation by their values j in the permutation yields the desired inverse.

p = [2, 1, 5, 0, 4, 3]

invert_permutation(p)
# [3, 1, 0, 5, 4, 2]

# inverse of inverse = identity
invert_permutation(invert_permutation(p)) == p
# True